Short answer
Both are portable players, $799 against $898.
The FiiO M15S reaches 100 dB on 566 of the 567 models here, the Sony NW-ZX707 on 550.
| Specification | FiiO M15S | Sony NW-ZX707 |
|---|---|---|
| Power into 32Ω | 580 mW | 25 mW |
| Power into 150Ω | 150 mW | 5.3 mW |
| Power into 300Ω | 93 mW | 2.7 mW |
| Power into 600Ω | 47 mW | 1.3 mW |
| Output impedance | 1.4 Ω | not published |
| Output noise | 3.2 µV | not published |
| Price | $799 | $898 |
| Headphones it reaches 100 dB on out of 567 | 566 | 550 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | FiiO M15S | Sony NW-ZX707 |
|---|---|---|
| Socket | 4.4mm (2.5mm also provided) | 4.4mm |
| Power into 32Ω | 1.2 W | 115 mW derived |
| Power into 300Ω | 368 mW | 12 mW derived |
| Output impedance | 2.3 Ω | not published |
| Output noise | 5.2 µV | not published |
| Headphones it reaches 100 dB on out of 567 | 567 | 561 |
Through the balanced sockets the FiiO M15S reaches 100 dB on 567 of the 567 models here and the Sony NW-ZX707 on 561. Derived figures are worked out from the loads the maker did publish.
| As published | FiiO M15S | Sony NW-ZX707 |
|---|---|---|
| DAC | ES9038PRO | not published |
| Processor | Snapdragon 660 | not published |
| 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) | 64 GB (actual available 47 GB); microSD / microSDHC / microSDXC |
| 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 stereo mini jack, 4.4 mm balanced standard jack |
| 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; transmission codecs SBC, LDAC, aptX, aptX HD, AAC |
| Wi-Fi | 2.4 GHz / 5 GHz, DLNA, AirPlay, Wi-Fi transmission, Roon Ready | IEEE 802.11 a/b/g/n/ac, 2.4 / 5 GHz |
| Formats | Native up to 384kHz-32bit / DSD256; USB audio 768kHz-32bit / DSD512 | WAV up to 32bit / 384kHz; FLAC 24bit / 384kHz; DSD 2.8224 / 5.6448 / 11.2896 MHz |
| Screen | 5.5-inch, 1440 x 720, full-fit | 5.0-inch (12.7 cm) TFT, HD 1280 x 720 |
| Battery life | 10.5 h (3.5 mm headphone output, volume 40) / 9 h (2.5 mm + 4.4 mm balanced output, volume 29) | Approx. 25 h (MP3 128kbps, stereo mini-jack, W.Music app) |
| Weight | 345 g | 227 g |
| Dimensions | About 140 x 80 x 18.9 mm | Approx. 72.5 x 132.3 x 16.9 mm (W x H x D) |
Copied from the makers’ own pages: fiio.com/m15s_parameters, fiio.com/m15s, sony-asia.com/electronics/support/digital-music-players-nw-nwz-zx-series/nw-zx707/specifications. Battery life is the maker’s own test figure.
| Load | FiiO M15S | Sony NW-ZX707 |
|---|---|---|
| 32 Ω | Published | Derived |
| 150 Ω | Derived | Derived |
| 300 Ω | Published | Derived |
| 600 Ω | Derived | Derived |
Only one of these two columns starts from a power rating. FiiO M15S publishes one at 32 Ω and at 300 Ω; Sony NW-ZX707 publishes none at any of these four loads, so its column is worked out from power it published at other loads. Both are arithmetic on a maker’s own figures rather than guesses, and the method used for the Sony NW-ZX707 understates rather than flatters — but at 32 Ω and at 300 Ω are the only loads here at which its maker can be held to a figure.
16 headphones reach 100 dB on the FiiO M15S but not on the Sony NW-ZX707 — Audio-Technica ATH-R70xa, Beyerdynamic DT 880 Edition (600Ω), Beyerdynamic DT 990 Edition (600Ω), 13 more.
550 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 Audio-Technica ATH-R70X: FiiO M15S has +16 dB of headroom there against +0 dB. 15 dB is about 35 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Sony NW-ZX707 because that maker publishes no output noise figure.
| Headphone | Impedance | Needs | FiiO M15S headroom | Sony NW-ZX707 headroom | FiiO M15S hiss | Sony NW-ZX707 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +39 dB damping | +28 dB | 25 dB | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +19 dB damping | +8 dB | 5 dB | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +26 dB | +12 dB | 3 dB | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +22 dB | +7 dB | -2 dB | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +18 dB | +6 dB | -3 dB | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +16 dB | +0 dB | -9 dB | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +11 dB | -4 dB | -13 dB | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +8 dB | -6 dB | -15 dB | not published |
The Sony NW-ZX707 costs $99 more than the FiiO M15S, and on these three axes the money buys nothing: among the 567 models here there is not one that the Sony NW-ZX707 handles and the FiiO M15S does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper FiiO M15S drives 16 models to 100 dB that the Sony NW-ZX707 does not.
Only published figures count here; blank axes are counted separately.
Each in full: FiiO M15S and Sony NW-ZX707.