Short answer
Both are portable players, $799 against $730.
On raw power they are level: each reaches 100 dB on 566 of the 567 non-electrostatic models here.
| Specification | FiiO M15S | FiiO M33 R2R |
|---|---|---|
| Power into 32Ω | 580 mW | 470 mW |
| Power into 150Ω | 150 mW | 109 mW |
| Power into 300Ω | 93 mW | 60 mW |
| Power into 600Ω | 47 mW | 30 mW |
| Output impedance | 1.4 Ω | 0.8 Ω |
| Output noise | 3.2 µV | 5.5 µV |
| Price | $799 | $730 |
| Headphones it reaches 100 dB on out of 567 | 566 | 566 |
| Balanced | FiiO M15S | FiiO M33 R2R |
|---|---|---|
| Socket | 4.4mm (2.5mm also provided) | 4.4mm |
| Power into 32Ω | 1.2 W | 1.1 W |
| Power into 300Ω | 368 mW | 240 mW |
| Output impedance | 2.3 Ω | 1.5 Ω |
| Output noise | 5.2 µV | 10.3 µV |
| Headphones it reaches 100 dB on out of 567 | 567 | 566 |
Through the balanced sockets the FiiO M15S reaches 100 dB on 567 of the 567 models here and the FiiO M33 R2R on 566.
| As published | FiiO M15S | FiiO M33 R2R |
|---|---|---|
| DAC | ES9038PRO | FiiO proprietary R2R DAC (fully differential 24-bit R2R resistor arrays) |
| Processor | Snapdragon 660 | Qualcomm Snapdragon 680 |
| Operating system | Android 10 | Android 13 |
| Storage | 64 GB storage (about 46 GB free), 4 GB RAM, single TF card slot up to 2 TB (theoretically) | 128 GB storage (about 112 GB usable), 8 GB RAM, memory card up to 2 TB |
| Outputs | 3.5 mm single-ended, 2.5 mm + 4.4 mm balanced, 3.5 mm line out (shared PO), 3.5 mm coaxial (shared PO) | 3.5 mm headphone out, 4.4 mm balanced headphone out, 3.5 mm line out (shared PO), 4.4 mm balanced line out (shared BAL), 3.5 mm coaxial (shared PO) |
| Bluetooth | Bluetooth 5.0; transmit SBC, AAC, aptX, aptX HD, LDAC, LHDC; receive SBC, AAC, aptX, aptX HD, aptX LL, LDAC, aptX Adaptive | Bluetooth 5.0; transmit SBC/aptX/aptX HD/LDAC/LHDC; receive SBC/LDAC |
| Wi-Fi | 2.4 GHz / 5 GHz, DLNA, AirPlay, Wi-Fi transmission, Roon Ready | 2.4 GHz / 5 GHz, DLNA / AirPlay / Wi-Fi music transfer |
| Formats | Native up to 384kHz-32bit / DSD256; USB audio 768kHz-32bit / DSD512 | Local up to 384kHz/32bit, DSD256 (Native); USB audio 768kHz/32bit, DSD512 |
| Screen | 5.5-inch, 1440 x 720, full-fit | 5.5-inch, 1080 x 2160, fully laminated |
| Battery | not published | 4400 mAh |
| Battery life | 10.5 h (3.5 mm headphone output, volume 40) / 9 h (2.5 mm + 4.4 mm balanced output, volume 29) | 15.5 h (3.5 mm headphone output) / 13.5 h (4.4 mm balanced output) |
| Weight | 345 g | 258 g |
| Dimensions | About 140 x 80 x 18.9 mm | About 138.2 x 71.5 x 17 mm |
Copied from the makers’ own pages: fiio.com/m15s_parameters, fiio.com/m15s, fiio.com/M33R2R_parameters, fiio.com/m33r2r. Battery life is the maker’s own test figure.
| Load | FiiO M15S | FiiO M33 R2R |
|---|---|---|
| 32 Ω | Published | Published |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Published |
| 600 Ω | Derived | Derived |
Both makers publish a power rating. FiiO M15S publishes at 32 Ω and at 300 Ω; FiiO M33 R2R 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.
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.
39 headphones are left alone by the FiiO M33 R2R under the one-eighth rule but coloured by the FiiO M15S (64 Audio Aspire 1, 64 Audio Fourte, 64 Audio Ocean, 36 more).
54 headphones stay below the audible-hiss threshold on the FiiO M15S but cross it on the FiiO M33 R2R (64 Audio Nio, 64 Audio U12t, 64 Audio U18s, 51 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 Sennheiser HD 600: FiiO M15S has +11 dB of headroom there against +10 dB. 2 dB is about 1.6 times the power, which matters for peaks rather than for how loud the music sits.
Hiss below about 20 dB SPL is inaudible in a quiet room.
| Headphone | Impedance | Needs | FiiO M15S headroom | FiiO M33 R2R headroom | FiiO M15S hiss | FiiO M33 R2R hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +39 dB damping | +39 dB | 25 dB | 29 dB |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +19 dB damping | +19 dB | 5 dB | 9 dB |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +26 dB | +24 dB | 3 dB | 7 dB |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +22 dB | +20 dB | -2 dB | 3 dB |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +18 dB | +18 dB | -3 dB | 2 dB |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +16 dB | +14 dB | -9 dB | -4 dB |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +11 dB | +10 dB | -13 dB | -8 dB |
| HiFiMAN Susvara | 60 Ω | 50 mW | +8 dB | +7 dB | -15 dB | -10 dB |
The FiiO M15S costs $69 more than the FiiO M33 R2R. Out of the 567 models here, that difference buys 54 more models kept below the audible-hiss threshold.
It does not run one way only: the cheaper FiiO M33 R2R leaves 39 models alone under the one-eighth rule that the FiiO M15S 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 M15S and FiiO M33 R2R.