Despite a typically rapid product lifecycle in the consumer audio market, FIIO’s K9 AKM digital-to-analog converter and headphone amplifier continues to resonate with audiophiles two years after its January 2024 launch. A detailed comparison within this article explores the K9 AKM’s enduring appeal-and its sonic differences-against the newer K15 and K17 models,all while charting the evolution of FIIO’s K9 series and its increasing focus on high-performance audio components. The analysis, based on rigorous testing, delves into the technical advancements and subjective listening experiences across the product line.
The FIIO K9 AKM, a USB DAC and headphone amplifier, launched in January 2024 and quickly gained a following among audiophiles. I purchased it shortly after a positive review, impressed by its sound quality.
Typically, products in this entry-level price range – around $900 at its initial release – have a limited lifespan, often superseded by newer models within a year. Long-term success is rare in this segment.
However, two years after its release, the K9 AKM continues to be discussed and remains an active model, even with the introduction of the K15 and K17.
In a market characterized by rapid turnover, the K9 AKM’s longevity is noteworthy. It prompted a comparison with its successors, the K15 and K17, to understand what sets it apart. This comparison explores the evolution of FIIO’s K9 series and its continued relevance in the competitive audio landscape.
A History of the K9 Series
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The K9 model line began with the K9 Pro LTD, released in December 2021, priced around $924. It featured an AKM AK4499EQ DAC chip and dual THX-AAA 788+ headphone amplifier circuits developed in collaboration between FIIO and THX.
In April 2022, the K9 Pro ESS arrived, swapping the AKM DAC chip for an ESS ES9038PRO, and priced around $1,293.
The K9 Pro ESS’s core design – including the THX-AAA 788+ amplifier circuits, dual-clock management, and ADC volume control – was carried forward into the K9, released in February 2023, priced around $798. The K9 aimed to maintain performance while reducing costs through a change to the ES9068AS DAC chip.
January 2024 saw the launch of the K9 AKM, priced around $891, featuring AKM’s flagship AK4191EQ+AK4499EX DAC. This DAC utilizes a separate digital and analog processing architecture. The shift from a single-chip DAC to a dual-chip configuration was a notable development, and the K9 AKM remains a popular choice.
The early adoption of this innovative two-chip DAC design in a desktop model was a key factor in its appeal, alongside its relatively affordable price point for a high-end DAC. This combination likely contributed to its sustained success.
My FIIO K9 AKM, used as a DAC for speaker systems.
In 2025, FIIO plans to release the K15 (around $988, featuring dual AK4497S DACs) and the K17 (around $1,650, with the AK4191EQ+AK4499EX configuration, but with a triple-chip setup including dual AK4499EX chips).
The K15, a successor to the K9, features a significantly updated design.
The K17, a successor to the K9 Pro series, shares a similar front panel design with the K15.
FIIO’s apparent preference for AKM DACs may be a matter of personal bias, but the company’s commitment to the technology is evident. The K19 (around $2,475), featuring a dual ESS ES9039PRO, represents the top-end of the K series. A comparison of the AKM and ESS DAC implementations would be a worthwhile endeavor for another time.
Redesigned K15 and K17
Let’s turn to the K15 (priced at $988).
K15
The K15 utilizes the AK4497S DAC chip, an upgrade from previous models. Along with the adoption of this latest chip, it includes a 10-band parametric equalizer (PEQ), bringing it closer in functionality to the K17.
The exterior design has been significantly updated. It features a color display capable of switching between various settings, and the power/output/gain switches have been replaced with more visible rotary controls. Volume and menu navigation are handled by a rotating dial.
The abundance of switches evokes a sense of nostalgia for older audio equipment. The display also offers options for analog-style meter displays.
The display defaults to a warm white panel reminiscent of incandescent lighting, but modern black-on-white options are also available.
A new feature is the inclusion of a 10-band high-precision lossless PEQ. It offers seven preset menus tailored to various music genres – jazz, rock, R&B, hip-hop, pop, dance, and classical – and allows for more detailed EQ adjustments through a dedicated app.
The K17 adds dynamic range compression, dynamic range expansion, a limiter, and compressor adjustment functions, enabling even more precise equalization. Other features include the ability to select six different digital filter characteristics offered by the DAC chip.
The menu system. Network settings and display customization are managed here.
EQ selection. Choose from seven presets or turn the EQ off.
Digital filter selection. Six filter characteristics are available.
The K15 replaces the K9 AKM’s THX-AAA 788+ amplifier circuit (maximum 2,000mW output) with a discrete AB-class headphone amplifier, capable of up to 3,000mW of balanced output.
The K17 utilizes a full discrete AB-class amplifier circuit without op-amps, delivering up to 4,000mW of balanced output. Compared to the K9 AKM’s maximum 2,000mW (balanced), this represents a significant increase in power.
Features a discrete AB-class headphone amplifier.
The power supply separates digital and analog power, and the analog side features a multi-stage power supply for each block – D/A conversion, low-pass filter, preamplifier, and output transistors.
The K17 shares a similar power supply architecture, but differs from the K15 by being AC power only, while the K15 supports both AC and DC power inputs.
Employs a multi-stage analog power supply.
The digital side features significantly improved clock performance, utilizing a femtosecond-precision ultra-low phase noise clock generator. The K15 incorporates two clocks for 48kHz and 44.1kHz systems, while the K17 adds a third clock dedicated to the AK4499EX.
Connectivity includes USB-A, USB-C, optical digital, and coaxial digital inputs, along with analog input/output and balanced outputs (4.4mm balanced and XLR). Uniquely, it features both an AC power inlet and a DC adapter port, catering to portable devices like DAPs.
It also includes a LAN port and supports Roon Ready and AirPlay, expanding connectivity and streaming options. The device supports PCM up to 768kHz/32bit, DSD512, and full MQA decoding. Combined with the EQ functions, the K9 series has seen substantial functional enhancements.
Rear panel view. The K17 is on the left, and the K15 is on the right. The K17 includes digital outputs, while the K15 has a DC power input.
Visually, the K17 is nearly identical to the K15. A comparison of the rear panels reveals that the K17 adds optical and coaxial digital outputs, while the K15 omits them but includes a DC power input. These differences suggest a focus on connectivity for desktop audio setups with the K17, and portability with the K15.
Beyond the price and resulting sound quality differences, the DC power input (K15) and digital output (K17) are the key distinctions between the two models. The other features are largely the same.
These enhancements to the digital circuitry, clocking, and amplifier circuits demonstrate a significant upgrade over the previous generation.
A full discrete AB-class headphone amplifier delivering 4,000mW of power.
The K17’s power supply.
K9 AKM, K15, and K17: Speaker Playback
Let’s begin testing. The K9 AKM, K15, and K17 are USB DAC-equipped headphone amplifiers, but I primarily use them as standalone DACs for speaker systems. Therefore, the initial test focused on speaker playback.
The speaker system consists of a Marantz AV 10, connected to the DAC via balanced outputs, and a Benchmark HP4 feeding BWV H-1 speakers. An Eclipse TD725SWMK2 subwoofer was also included.
The BWV H-1 speakers are stacked, and I recently implemented DIRAC LIVE ART in my listening room. The results were impressive, and 2.1-channel playback with the subwoofer proved superior to stereo playback alone.
The addition of the subwoofer significantly enhanced low-frequency reproduction, minimizing standing waves and improving both resolution and overall clarity. I plan to cover DIRAC LIVE ART in a separate article if there’s sufficient interest.
Speaker playback utilizes a 2.1-channel setup with BWV H-1 speakers and four Eclipse TD725SWMK2 subwoofers.
Playback was handled by a first-generation LINN MAJIK DS player, connected to the DAC via optical digital output.
I started with the third movement of Tchaikovsky’s Symphony No. 6 “Pathétique,” opting for a recording by Vladimir Fedoseyev and the Moscow Radio Symphony Orchestra, recently discovered. The performance is faster-paced and more energetic than the familiar recording by Kurt Masur and Musica Aeterna.
First, the K9 AKM. The performance is crisp and dynamic, with a powerful and impactful balance. The soundstage and depth are present, but not exceptionally wide. The tempo and energy are well-defined, delivering a sense of scale and impact. Compared to the K15 and K17, it has a slightly warmer, more energetic sound.
Next, the K15. The sound is refined and high-quality. It sounds quieter than the K9 AKM, and the volume seems slightly reduced. However, the number of instruments is increased, and the separation of individual sounds is improved. The depth of the soundstage is also greater. The subtle resonance of instruments in the back of the stage is clearly audible.
The K15 offers a significant increase in information, delivering a precise and detailed performance.
Finally, the K17. The soundstage is expansive, the granularity of individual sounds is excellent, and the resolution is remarkable. It doesn’t sound overly high-resolution, but each sound has a soft outline and fine detail.
The sound is natural and high-quality, similar to the K15, but with added power and impact. The grandeur of the fortissimo passages is fully realized. Compared to the K9 AKM, the K15 and K17 represent a substantial advancement in audio performance.
I then played Musorgsky’s “The Hut on Chicken Legs” from “Pictures at an Exhibition,” performed by Dudamel and the Vienna Philharmonic. It’s a powerful piece that evokes a sense of strength and intensity rather than fear.
The K9 AKM delivers a strong sense of energy and a thick sound image. The soundstage is present, but not exceptionally wide. The tempo and speed are well-defined, and the impact is significant.
The K15 offers a more subdued and refined sound. The tempo and speed are slightly softened, but the subtle resonance of low-frequency instruments is beautifully reproduced. The sound is less forceful than the K9 AKM, but the texture is excellent.
The K17 delivers both power and speed, capturing the dynamism and excitement of the performance. It provides a strong sense of impact and a clear representation of both quiet and loud passages.
While the K9 AKM delivers impact, the K15 and K17 offer a more refined and detailed sound. The K17, in particular, combines power with precision, delivering a remarkably detailed and impactful performance.
All three DACs utilize AKM chips, with the K15 featuring the single-chip AK4497S, and the K9 AKM and K17 using the AK4191EQ+AK4499EX configuration. The dual AK4499EX chips in the K17 are a key difference.
While there are common sonic characteristics due to the AKM chips, the differences in the audio circuitry and amplifier circuits are significant. FIIO has also demonstrably improved its ability to leverage the DAC’s potential. The latest models clearly offer a performance advantage.
K9 AKM, K15, and K17: Headphone Playback
Now, let’s move on to headphone playback. I used an Astell&Kern PD10 player, connected via USB audio output to the K9 AKM/K15/K17’s balanced outputs. Gain, volume, and audio filter settings were kept consistent across all three devices. I used SENDYAUDIO’s Peacock headphones for the test.
Playing Tchaikovsky’s Symphony No. 6 through the headphones, the planar magnetic drivers of the Peacock headphones deliver a wide soundstage and a natural, immersive listening experience.
The sound image is soft, but the sense of impact and the resonance of the bass drum are clearly reproduced. The headphones accurately convey the vibration of the drumhead and the resonance of the body. The soundstage is wide and spacious, and the subtle nuances of the music are well-defined.
I’m a fan of the THX-AAA circuitry, and these amplifiers drive the headphones effectively.
Next, the K15. The overall sound is clear, with a wide and well-defined soundstage. The granularity of individual sounds is excellent, with no trace of the slight muddiness I noticed with the K9 AKM.
While the power output feels sufficient, it’s slightly more subdued than the K9 AKM. However, the increased information and refined sound quality are noticeable. The soundstage is deeper, and the subtle details are more apparent. It’s a more mature and refined sound.
Finally, the K17. The soundstage is even wider, the texture of individual sounds is richer, and the resolution is exceptional. It doesn’t sound overly analytical, but each sound has a soft outline and fine detail.
The sound is natural and high-quality, similar to the K15, but with improved power, speed, and responsiveness. The dynamic range and emotional impact of the music are enhanced.
In terms of audio quality improvements, the K15 and K17 clearly demonstrate the benefits of technological advancements and performance enhancements.
I then played “JANE DOE” by Kenshi Yonezu and Utada Hikaru.
The K9 AKM delivers a strong sense of vocal energy and thickness. The texture of each voice is well-defined, and the nuances of their delivery are accurately reproduced. The ample bass and expansive accompaniment are characteristic of modern pop music, creating an immersive soundscape.
The K15 produces a smoother, more refined vocal reproduction. The voices are delicate and elegant. While it lacks the raw power of the K9 AKM, it doesn’t feel lacking. The texture and subtle differences in their singing styles are clearly discernible. The rhythm of the accompaniment is slightly more restrained, but it’s still impactful and responsive.
The K17 enhances the presence and physicality of the vocals, placing them prominently in a wide and expansive soundstage. The arrangement suggests a close, intimate connection between the two singers, yet also a sense of distance and detachment.
The subtle nuances of their relationship and distance are palpable, creating a captivating and sensual performance. The vocal texture and breathiness are exceptionally well-reproduced.
The K15 and K17 Show Clear Progress, While the K9 AKM Remains Appealing
The comparison clearly demonstrates that the K15 and K17 represent significant advancements.
FIIO has established itself as a popular brand, gaining recognition for its performance and value. Initially, it was known for its affordable, easy-to-listen-to sound. The slightly warm, energetic sound signature was a defining characteristic. I’ve always appreciated this as part of FIIO’s identity.
As the brand’s reputation grew, it focused on refining its sound and improving its audio performance, a positive evolution.
If I were making a purchase today, I would confidently recommend the K17. If budget is a concern, the K15 is also a strong contender. Both offer significant improvements in audio performance and functionality, and are aesthetically pleasing.
However, when asked if I would upgrade from the K9 AKM, I hesitate. The K9 AKM possesses a unique appeal that the K15 and K17 haven’t fully replicated.
The K9 AKM launched during a period when FIIO was establishing itself as a brand known for its value, sound quality, and audio performance.
The slight warmth and energetic character that remains in the K9 AKM may be considered a flaw by some, but I find it appealing. The K9 AKM continues to be sold, demonstrating its enduring appeal. Whether it’s a lucky find or a product with lasting qualities is debatable. I’m hesitant to offer a definitive opinion.
FIIO could explore adding a unique sonic character to the K15 and K17, while maintaining their high performance. It could be a subtle coloration or a distinctive signature sound. This is a challenge for FIIO as it continues to grow as an audio manufacturer.
Ultimately, FIIO’s commitment to offering high-quality products at accessible prices is commendable. The ability to choose between several excellent models in the $1,000 price range is a benefit to consumers.
If you’re looking for a DAC-equipped headphone amplifier in this price range, or are simply curious, I encourage you to listen to the three models (and the K19) and discover what suits your preferences. It’s a rewarding experience.
