Short answer
Both are portable players, $750 against $898.
The HiBy R6 Pro II reaches 100 dB on 566 of the 567 models here, the Sony NW-ZX707 on 550.
| Specification | HiBy R6 Pro II | Sony NW-ZX707 |
|---|---|---|
| Power into 32Ω | 750 mW | 25 mW |
| Power into 150Ω | 280 mW | 5.3 mW |
| Power into 300Ω | 140 mW | 2.7 mW |
| Power into 600Ω | 70 mW | 1.3 mW |
| Output impedance | 0.6 Ω unverified | not published |
| Output noise | 4 µV unverified | not published |
| Price | $750 | $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 | HiBy R6 Pro II | Sony NW-ZX707 |
|---|---|---|
| Socket | no separate rating | 4.4mm |
| Power into 32Ω | — | 115 mW derived |
| Power into 300Ω | — | 12 mW derived |
| Output impedance | — | not published |
| Output noise | — | not published |
| Headphones it reaches 100 dB on out of 567 | — | 561 |
Only the Sony NW-ZX707 has a separate balanced rating from its maker; through it, it reaches 100 dB on 561 of the 567 models here. The HiBy R6 Pro II may still have a balanced socket — its spec sheet simply gives no figure for one, so there is nothing to put beside it. Derived figures are worked out from the loads the maker did publish.
| Load | HiBy R6 Pro II | Sony NW-ZX707 |
|---|---|---|
| 32 Ω | Unverified | Derived |
| 150 Ω | Unverified | Derived |
| 300 Ω | Unverified | Derived |
| 600 Ω | Unverified | Derived |
HiBy R6 Pro II publishes no electrical specification at all. That is true of 10 of the 280 sources here, and the figures in that column come from independent measurement rather than from a maker document — which is not worse, but it is not the same thing, and it cannot be checked against anything the maker will stand behind.
The Sony NW-ZX707 column stands on figures its maker printed, but not at these loads — every row of it is worked out from power published somewhere else. Reading the two straight across sets one kind of claim against another, and nobody has written down the conditions of both side by side.
16 headphones reach 100 dB on the HiBy R6 Pro II 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: HiBy R6 Pro II has +18 dB of headroom there against +0 dB. 17 dB is about 53 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for HiBy R6 Pro II and Sony NW-ZX707 because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | HiBy R6 Pro II headroom | Sony NW-ZX707 headroom | HiBy R6 Pro II hiss | Sony NW-ZX707 hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +37 dB | +28 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +17 dB | +8 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +27 dB | +12 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +24 dB | +7 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +19 dB | +6 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +18 dB | +0 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +13 dB | -4 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +10 dB | -6 dB | not published | not published |
The Sony NW-ZX707 costs $148 more than the HiBy R6 Pro II, 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 HiBy R6 Pro II does not — not on power, not on the one-eighth rule, not on hiss. The traffic runs the other way: the cheaper HiBy R6 Pro II drives 16 models to 100 dB that the Sony NW-ZX707 does not.
Only published figures count here; blank axes are counted separately.
Each has a page of its own with a full headphone list and the provenance of every figure — worth opening here, because HiBy R6 Pro II has published no electrical specification at all and everything above comes from independent measurement: HiBy R6 Pro II and Sony NW-ZX707.