Short answer
Both are dongles, $149 against $109.
On raw power they are level: each reaches 100 dB on 564 of the 567 non-electrostatic models here.
| Specification | FiiO KA17 | Onix Alpha XI1 |
|---|---|---|
| Power into 32Ω | 140 mW | 180 mW |
| Power into 150Ω | 34 mW | 38 mW |
| Power into 300Ω | 20 mW | 19 mW |
| Power into 600Ω | 10.0 mW | 9.6 mW |
| Output impedance | 1.0 Ω | 0.4 Ω |
| Output noise | 2.0 µV | not published |
| Price | $149 | $109 |
| Headphones it reaches 100 dB on out of 567 | 564 | 564 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | FiiO KA17 | Onix Alpha XI1 |
|---|---|---|
| Socket | 4.4mm | 4.4mm |
| Power into 32Ω | 300 mW | 500 mW |
| Power into 300Ω | 30 mW | 53 mW derived |
| Output impedance | 1.5 Ω | 0.8 Ω |
| Output noise | 2.2 µV | not published |
| Headphones it reaches 100 dB on out of 567 | 565 | 566 |
Through the balanced sockets the Onix Alpha XI1 reaches 100 dB on 566 of the 567 models here and the FiiO KA17 on 565. Derived figures are worked out from the loads the maker did publish.
| Load | FiiO KA17 | Onix Alpha XI1 |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Derived |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. FiiO KA17 publishes at 32 Ω and at 300 Ω; Onix Alpha XI1 at 32 Ω. The other rows are worked out from those.
So the two columns are not equally firm row by row: at 300 Ω only the FiiO KA17 figure is the maker’s own. On those rows the derived number is the one to doubt first.
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 Onix Alpha XI1 under the one-eighth rule but coloured by the FiiO KA17 (64 Audio Nio, 64 Audio Volur, Campfire Audio Andromeda 2023, 11 more).
564 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 HiFiMAN Susvara: Onix Alpha XI1 has +3 dB of headroom there against +2 dB. 1 dB is about 1.2 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Onix Alpha XI1 because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | FiiO KA17 headroom | Onix Alpha XI1 headroom | FiiO KA17 hiss | Onix Alpha XI1 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +32 dB | +31 dB | 20 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +12 dB | +11 dB | 0 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +19 dB | +20 dB | -1 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +16 dB | +16 dB | -6 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +12 dB | +12 dB | -7 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +9 dB | +9 dB | -13 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +5 dB | +5 dB | -17 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +2 dB | +3 dB | -19 dB | not published |
The FiiO KA17 costs $40 more than the Onix Alpha XI1, and on these three axes the money buys nothing: among the 567 models here there is not one that the FiiO KA17 handles and the Onix Alpha XI1 does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper Onix Alpha XI1 leaves 14 models alone under the one-eighth rule that the FiiO KA17 does not.
Only published figures count here; blank axes are counted separately.
Each in full: FiiO KA17 and Onix Alpha XI1.