Short answer
Both are portable players, $799 against $1149.
On raw power they are level: each reaches 100 dB on 566 of the 567 non-electrostatic models here.
| Specification | FiiO M15S | iBasso DX270 |
|---|---|---|
| Power into 32Ω | 580 mW | 416 mW |
| Power into 150Ω | 150 mW | 89 mW |
| Power into 300Ω | 93 mW | 44 mW |
| Power into 600Ω | 47 mW | 22 mW |
| Output impedance | 1.4 Ω | 0.5 Ω |
| Output noise | 3.2 µV | not published |
| Price | $799 | $1149 |
| Headphones it reaches 100 dB on out of 567 | 566 | 566 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | FiiO M15S | iBasso DX270 |
|---|---|---|
| Socket | 4.4mm (2.5mm also provided) | 4.4mm |
| Power into 32Ω | 1.2 W | 1.6 W |
| Power into 300Ω | 368 mW | 168 mW derived |
| Output impedance | 2.3 Ω | 0.7 Ω |
| Output noise | 5.2 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. Derived figures are worked out from the loads the maker did publish.
| Load | FiiO M15S | iBasso DX270 |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Derived |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. FiiO M15S publishes at 32 Ω and at 300 Ω; iBasso DX270 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 M15S 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.
50 headphones are left alone by the iBasso DX270 under the one-eighth rule but coloured by the FiiO M15S (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Nio, 47 more).
566 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 M15S has +19 dB of headroom there against +15 dB. 4 dB is about 2.6 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for iBasso DX270 because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | FiiO M15S headroom | iBasso DX270 headroom | FiiO M15S hiss | iBasso DX270 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +39 dB damping | +35 dB | 25 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +19 dB damping | +15 dB | 5 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +26 dB | +24 dB | 3 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 | +18 dB | +16 dB | -3 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +16 dB | +13 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 | +6 dB | -15 dB | not published |
The iBasso DX270 costs $350 more than the FiiO M15S. Out of the 567 models here, that difference buys 50 more models left alone under the one-eighth rule.
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.
Each in full: FiiO M15S and iBasso DX270.