Short answer
Both are portable amplifiers, $440 against $599.
The FiiO Q15 reaches 100 dB on 567 of the 567 models here, the iFi xDSD Gryphon on 565.
| Specification | FiiO Q15 | iFi xDSD Gryphon |
|---|---|---|
| Power into 32Ω | 625 mW | 320 mW |
| Power into 150Ω | 149 mW | 73 mW |
| Power into 300Ω | 85 mW | 40 mW |
| Power into 600Ω | 43 mW | 20 mW |
| Output impedance | 1.0 Ω | 1.0 Ω |
| Output noise | 3.1 µV | not published |
| Price | $440 | $599 |
| Headphones it reaches 100 dB on out of 567 | 567 | 565 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | FiiO Q15 | iFi xDSD Gryphon |
|---|---|---|
| Socket | 4.4mm | 4.4mm |
| Power into 32Ω | 1.6 W | 1.0 W |
| Power into 300Ω | 340 mW | 125 mW derived |
| Output impedance | 1.5 Ω | 1.0 Ω |
| Output noise | 3.1 µV | not published |
| Headphones it reaches 100 dB on out of 567 | 567 | 566 |
Through the balanced sockets the FiiO Q15 reaches 100 dB on 567 of the 567 models here and the iFi xDSD Gryphon on 566. Derived figures are worked out from the loads the maker did publish.
| Load | FiiO Q15 | iFi xDSD Gryphon |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. FiiO Q15 publishes at 32 Ω and at 300 Ω; iFi xDSD Gryphon 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.
2 headphones reach 100 dB on the FiiO Q15 but not on the iFi xDSD Gryphon — Moondrop PARA, Symphonium Titan.
565 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 Q15 has +20 dB of headroom there against +14 dB. 7 dB is about 4.7 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for iFi xDSD Gryphon because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | FiiO Q15 headroom | iFi xDSD Gryphon headroom | FiiO Q15 hiss | iFi xDSD Gryphon hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +40 dB | +34 dB | 24 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +20 dB | +14 dB | 4 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +26 dB | +23 dB | 2 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +22 dB | +19 dB | -2 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +19 dB | +15 dB | -3 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +15 dB | +12 dB | -9 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +11 dB | +8 dB | -13 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +8 dB | +5 dB | -15 dB | not published |
The iFi xDSD Gryphon costs $159 more than the FiiO Q15, and on these three axes the money buys nothing: among the 567 models here there is not one that the iFi xDSD Gryphon handles and the FiiO Q15 does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper FiiO Q15 drives 2 models to 100 dB that the iFi xDSD Gryphon does not.
Only published figures count here; blank axes are counted separately.
Each in full: FiiO Q15 and iFi xDSD Gryphon.