Short answer
Both are portable players, $1799 against $1599.
The FiiO M17 reaches 100 dB on 567 of the 567 models here, the iBasso DX320 on 565.
| Specification | FiiO M17 | iBasso DX320 |
|---|---|---|
| Power into 32Ω | 500 mW | 380 mW |
| Power into 150Ω | 115 mW | 81 mW |
| Power into 300Ω | 63 mW | 40 mW |
| Power into 600Ω | 32 mW | 20 mW |
| Output impedance | 1 Ω | 0.34 Ω |
| Output noise | 3.5 µV | not published |
| Price | $1799 | $1599 |
| 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 M17 | iBasso DX320 |
|---|---|---|
| Socket | 4.4mm | 4.4mm |
| Power into 32Ω | 3.0 W | 1.2 W |
| Power into 300Ω | 250 mW | 168 mW |
| Output impedance | 2 Ω | 0.38 Ω |
| Output noise | 7 µV | not published |
| 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 M17 | iBasso DX320 |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. FiiO M17 publishes at 32 Ω and at 300 Ω; iBasso DX320 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 M17 but not on the iBasso DX320 — Moondrop PARA, Symphonium Titan.
15 headphones are left alone by the iBasso DX320 under the one-eighth rule but coloured by the FiiO M17 (64 Audio Nio, 64 Audio Volur, Campfire Audio Andromeda 2023, 12 more).
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 M17 has +20 dB of headroom there against +14 dB. 6 dB is about 3.9 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for iBasso DX320 because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | FiiO M17 headroom | iBasso DX320 headroom | FiiO M17 hiss | iBasso DX320 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +40 dB | +34 dB | 25 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +20 dB | +14 dB | 5 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +25 dB | +23 dB | 3 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +21 dB | +19 dB | -1 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +19 dB | +16 dB | -2 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +14 dB | +12 dB | -8 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +10 dB | +8 dB | -12 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +7 dB | +6 dB | -14 dB | not published |
The FiiO M17 costs $200 more than the iBasso DX320. Out of the 567 models here, that difference buys 2 more models driven to 100 dB.
It does not run one way only: the cheaper iBasso DX320 leaves 15 models alone under the one-eighth rule that the FiiO M17 does not, which is the part worth checking against your own headphones before paying the difference.
Only published figures count here; blank axes are counted separately.
Each in full: FiiO M17 and iBasso DX320.