Short answer
Both are desktop DAC/amps, $990 against $1430.
On raw power they are level: each reaches 100 dB on 567 of the 567 non-electrostatic models here.
| Specification | FiiO K17 | FiiO K19 |
|---|---|---|
| Power into 32Ω | 1.9 W | 2.3 W |
| Power into 150Ω | 431 mW | 512 mW |
| Power into 300Ω | 240 mW | 270 mW |
| Power into 600Ω | 120 mW | 135 mW |
| Output impedance | 1.0 Ω | 0.6 Ω |
| Output noise | 5.0 µV | 3.5 µV |
| Price | $990 | $1430 |
| Headphones it reaches 100 dB on out of 567 | 567 | 567 |
| Balanced | FiiO K17 | FiiO K19 |
|---|---|---|
| Socket | 4.4mm / XLR4 | 4.4mm / XLR4 |
| Power into 32Ω | 4.0 W | 8.0 W |
| Power into 300Ω | 950 mW | 1.1 W |
| Output impedance | 1.5 Ω | 0.6 Ω |
| Output noise | 7.9 µV | 6.0 µV |
| Headphones it reaches 100 dB on out of 567 | 567 | 567 |
Through the balanced sockets the two are level on the same test: each reaches 100 dB on 567 of the 567 models here.
| Load | FiiO K17 | FiiO K19 |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. FiiO K17 publishes at 32 Ω and at 300 Ω; FiiO K19 at 32 Ω and at 300 Ω. The other rows are worked out from those.
The two publish at the same loads, which is the one case where the rows of this table can be read straight across.
On power they are interchangeable across this whole database: there is no headphone here that one reaches 100 dB on and the other does not.
14 headphones are left alone by the FiiO K19 under the one-eighth rule but coloured by the FiiO K17 (64 Audio Nio, 64 Audio Volur, Campfire Audio Andromeda 2023, 11 more).
35 headphones stay below the audible-hiss threshold on the FiiO K19 but cross it on the FiiO K17 (64 Audio Nio, 64 Audio U12t, 64 Audio U18s, 32 more).
567 of the 567 models here reach 100 dB on both.
Headroom is at a 100 dB SPL peak.
The widest gap on the list is the Campfire Audio Andromeda 2020: FiiO K19 has +28 dB of headroom there against +24 dB. 3 dB is about 2.2 times the power, which matters for peaks rather than for how loud the music sits.
Hiss below about 20 dB SPL is inaudible in a quiet room.
| Headphone | Impedance | Needs | FiiO K17 headroom | FiiO K19 headroom | FiiO K17 hiss | FiiO K19 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +44 dB | +48 dB | 28 dB | 25 dB |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +24 dB | +28 dB | 8 dB | 5 dB |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +30 dB | +31 dB | 7 dB | 3 dB |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +26 dB | +27 dB | 2 dB | -1 dB |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +24 dB | +25 dB | 1 dB | -2 dB |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +20 dB | +20 dB | -5 dB | -8 dB |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +16 dB | +16 dB | -9 dB | -12 dB |
| HiFiMAN Susvara | 60 Ω | 50 mW | +13 dB | +14 dB | -11 dB | -14 dB |
The FiiO K19 costs $440 more than the FiiO K17. Out of the 567 models here, that difference buys 14 more models left alone under the one-eighth rule and 35 more models kept below the audible-hiss threshold.
Nothing runs the other way: there is no axis here on which the cheaper of the two does better.
Only published figures count here; blank axes are counted separately.