Both are portable players, $799 against $1799. This page puts them side by side on the only three things a maker can be held to — power, output impedance and noise — and then asks the question that actually matters: which headphones do they treat differently?
The FiiO M27 reaches 100 dB on 567 of the 567 models here, the FiiO M15S on 566.
| Specification | FiiO M15S | FiiO M27 |
|---|---|---|
| Power into 32Ω | 580 mW | 1.8 W |
| Power into 150Ω | 150 mW | 391 mW |
| Power into 300Ω | 93 mW | 200 mW |
| Power into 600Ω | 47 mW | 100 mW |
| Output impedance | 1.4 Ω | 0.5 Ω |
| Output noise | 3.2 µV | 3.9 µV |
| Price | $799 | $1799 |
| Headphones it reaches 100 dB on out of 567 | 566 | 567 |
A figure marked not published is missing from the maker’s own material, which is not the same as being good or bad. Where one of these two publishes a number and the other does not, the comparison on that axis cannot be made at all — and saying so is more useful than guessing.
1 headphone reaches 100 dB on the FiiO M27 but not on the FiiO M15S — Symphonium Titan.
50 headphones are left alone by the FiiO M27 under the one-eighth rule but coloured by the FiiO M15S (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Nio, 47 more).
14 headphones stay below the audible-hiss threshold on the FiiO M15S but cross it on the FiiO M27 (Audio-Technica ATH-CKS1100, Austrian Audio Hi-X25BT, Beyerdynamic DJ 300 PRO X, 11 more).
566 of the 567 models here reach 100 dB on both. That is a power count and nothing more; whether either source suits a given headphone also depends on the two lines above.
Each has a page of its own with every power figure traced to what the maker published and a full headphone list: FiiO M15S and FiiO M27. Or put either against your own headphones in the source comparison tool.