By aspect — in detail
Transparency
Contested · 9 srcSources split, and this is the canonical electronics argument in miniature. One camp reports the K9 AKM measures and reads as neutral — that the converter swap is a spec-sheet event, not a sonic one. The other hears a consistent, repeatable character next to the ESS-chipped K9: warmer, rounder, less etched, more forgiving of poor recordings. Notably the two camps agree on the direction of the claimed difference; they disagree only on whether it is real.
Measured
FiiO publishes line-out THD+N below 0.00020% with SNR at or above 128 dB on the balanced output (0.00026%/127 dB from the 6.35 mm headphone jack), figures that sit at or past the point most listening can resolve. Nothing in the published data distinguishes the AKM version tonally from the ES9068AS K9.
⚠ vs. listeners — The numbers say both K9 variants are transparent; several reviewers who heard them side by side describe the same directional difference anyway. The most instructive evidence comes from the strongest believer: the r/headphones owner whose enthusiastic first impressions started the biggest thread on this unit was challenged to test it properly, swapped the DAC and amp sections between a K7 and a K9 AKM, and reported back that 'The differences are very subtle,' and that implementation and the power supply seemed to matter more than the converter. A heavily upvoted reply in that same thread put the skeptical case bluntly — 'It's a dead flat, dead silent 100% transparent device that has absolutely no impact on the frequency response of a headphone.' No published blind test settles it.
Where it splits
Neutral and transparent — the converter swap is a spec difference, not a sound57%
“This is a neutral DAC/amp with excellent tonal balance, unquestionable transparency and mirror-like fidelity.”
Ichos · Head-Fi
Audibly warmer and richer than the ESS version — a real house character43%
“the K9 AKM leans towards a warmer, richer signature DAC sound with a bit of coloration”
Headfonics
Sources split, but along a load boundary rather than a matter of taste. Through about 300 Ω everyone reports abundant headroom — HD 600/650, HD 660S2, FT3, Ananda Nano, HE1000 Stealth all come up as comfortably driven. The reviewers who find it short are all reaching past that: a 600 Ω AKG 240DF, an HE6se v2, a Susvara. That boundary is not a mystery — it is roughly where FiiO's own recommended load range stops.
Measured
FiiO rates the balanced output at 2,000 mW + 2,000 mW into 32 Ω and 780 mW + 780 mW into 300 Ω, and the 6.35 mm single-ended output at 1,500 mW into 32 Ω but only 200 mW into 300 Ω. Output impedance is under 1 Ω on both. Three gain settings; peak output swing above 42 Vp-p balanced.
⚠ vs. listeners — FiiO's marketing says that 'No matter if you use low-impedance or high-impedance headphones, the K9 AKM will drive it with aplomb,' but its own parameter table lists a recommended load range of 8–350 Ω balanced and just 8–150 Ω single-ended. The reviewers who report running short are all above that line, which suggests the disagreement is less about ears than about which side of FiiO's own stated ceiling each listener was working on. The single-ended jack is the weaker half by a wide margin.
Where it splits
Plenty of headroom for anything most people own64%
“The Nano loves extra oomph, and the K9 AKM has plenty of juice to spare.”
Headfonia
Runs out on genuinely hard loads — very high impedance and the insensitive planars36%
“Once you move past that level of impedance, the K9 AKM struggles a bit.”
Headfonics
The widest split in the set, and it is really a disagreement about what you are buying. Reviewers who weigh the whole package — chassis, linear supply, the I/O, Bluetooth, three headphone outputs — call it a lot of hardware for the money and rate it above its siblings. The measurement-minded reply that a far cheaper DAC will measure the same and that the built-in amp is redundant if you already own one. A returning owner adds a third angle: at this price the software polish should be better than a box costing a third as much.
Where it splits
A lot of box for the money — the all-in-one is the value59%
“Excellent price to performance ratio”
Headfonia
You are paying for features, not sound — cheaper gear measures the same41%
“No reason to pay extra for the FiiO's built-in Headphone Amp if you're planning on using an external one anyway.”
staticV3 · Audio Science Review
Noise
Strong consensus · 7 srcThe most consistent praise in the set. Reviewers using very sensitive IEMs report an inaudible floor, and the low output impedance keeps multi-driver IEMs from being tonally skewed. The only recorded caveat is narrow: one reviewer heard a faintly less-than-black background on high gain with a single planar IEM, and none below high gain.
“The background, similar to the K9, is pitch-black.”
Headfonia
“Background noise is inaudible even with very sensitive earphones such as the FiiO FX15.”
Ichos · Head-Fi
Measured
FiiO rates the noise floor at under 3.0 µV single-ended and under 5.2 µV balanced (A-weighted), with SNR at or above 127 dB and 124 dB respectively, and output impedance under 1 Ω into 32 Ω. Attenuation is done by a pair of NJU72315 volume ICs rather than by the knob itself, which FiiO credits for the low channel deviation across its 120 volume steps.
Mostly agreement, with a specific and repeated exception. The connector count is the headline — three headphone outputs, RCA and XLR line/pre-out, USB-B plus a side USB-C, coax, optical, and a 4.4 mm balanced line-in that is genuinely rare at the price — alongside Bluetooth 5.1 with LDAC, three gain settings and separate DAC, pre-out and headphone modes. The exception is the app: the parametric EQ works only on the Bluetooth input, and there is no remote and no volume control in the app, which several reviewers name as the one thing keeping it off the top of the class.
“Also, there is a 4.4mm input on the back, a rare feature in this price range.”
Headfonia
“Unfortunately the EQ is only effective in Bluetooth reception mode.”
Ichos · Head-Fi
Measured
Inputs: USB-B, side USB-C, coaxial, optical, RCA and 4.4 mm balanced line-in. Outputs: 6.35 mm, 4.4 mm and 4-pin XLR headphone, plus RCA and XLR line or pre-out. Bluetooth 5.1 receive-only via a QCC5124, supporting LDAC, aptX Adaptive/HD/LL, AAC and SBC. Up to 768 kHz/32-bit PCM and DSD512 over USB; UAC 1.0 and 2.0 modes. FiiO's own product page footnotes the EQ: 'This function is only valid for Bluetooth decoding.'
Consistently praised. A 2.66 kg sandblasted CNC aluminium chassis with an internal linear transformer, gold-plated connectors, an included vertical stand, and a temperature that owners describe as warm rather than hot. The recorded negatives are minor and cosmetic — the matte finish shows fingerprints and the front-panel lettering is small in dim light — with one genuine outlier: an owner on the official thread reported the unit dropping to a red status ring and silence a few weeks in, and referred to other owners hitting the same fault.
“The build quality is exemplary. It is sturdy, durable, and meticulously assembled.”
Headfonia
“This piece has substantial weight, plus the finish quality is exceptional.”
Audio Pursuit
Ergonomics
Moderate · 8 srcSplit by layer rather than by opinion: reviewers like the metal and dislike the software. The volume knob draws some of the strongest praise in the set — 120 steps with no sudden jumps in level — and the switch-and-LED front panel is learned in minutes. Against that sit a set of recurring niggles: no volume readout in a dark room, no remote, a knob some wish were detented, occasional Bluetooth pairing struggles, and settings such as the LED ring that revert on every power cycle. It is a big, heavy unit that takes real desk space unless you stand it up.
“This is one of the smoothest operating volume knobs I have used.”
Headfonics
“Does not remember setting from the app to turn off the RGB. I have to turn it off after every single power cycle.”
u/ExxInferis · r/FiiO
Measured
Volume is an analogue potentiometer read by an ADC driving an NJU72315 volume IC across 120 steps, with channel balance adjustable L12 to R12 in 0.5 dB increments. The unit measures 200 × 224.5 × 72 mm and weighs about 2,660 g, and ships with a stand for vertical placement.
