Short answer
Both are portable players, $649 against $750.
The HiBy R6 Pro II reaches 100 dB on 566 of the 567 models here, the Cayin N3 Ultra on 565.
| Specification | Cayin N3 Ultra | HiBy R6 Pro II |
|---|---|---|
| Power into 32Ω | 250 mW | 750 mW |
| Power into 150Ω | 53 mW | 280 mW |
| Power into 300Ω | 27 mW | 140 mW |
| Power into 600Ω | 13 mW | 70 mW |
| Output impedance | 0.5 Ω | 0.6 Ω unverified |
| Output noise | not published | 4 µV unverified |
| Price | $649 | $750 |
| Headphones it reaches 100 dB on out of 567 | 565 | 566 |
Not published means the maker leaves it out, so that axis cannot be compared.
| Balanced | Cayin N3 Ultra | HiBy R6 Pro II |
|---|---|---|
| Socket | 4.4mm | no separate rating |
| Power into 32Ω | 600 mW | — |
| Power into 300Ω | 64 mW derived | — |
| Output impedance | 1 Ω | — |
| Output noise | not published | — |
| Headphones it reaches 100 dB on out of 567 | 566 | — |
Only the Cayin N3 Ultra has a separate balanced rating from its maker; through it, it reaches 100 dB on 566 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 | Cayin N3 Ultra | HiBy R6 Pro II |
|---|---|---|
| 32 Ω | Published | Unverified |
| 150 Ω | Derived | Unverified |
| 300 Ω | Derived | Unverified |
| 600 Ω | Derived | Unverified |
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 Cayin N3 Ultra column does stand on a power rating its maker printed, at one of these four loads at least. Reading the two straight across sets one kind of claim against another, and nobody has written down the conditions of both side by side.
1 headphone reaches 100 dB on the HiBy R6 Pro II but not on the Cayin N3 Ultra — Moondrop PARA.
565 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 +10 dB. 7 dB is about 5.3 times the power, which matters for peaks rather than for how loud the music sits.
The hiss columns are empty for Cayin N3 Ultra and HiBy R6 Pro II because neither maker publishes no output noise figure.
| Headphone | Impedance | Needs | Cayin N3 Ultra headroom | HiBy R6 Pro II headroom | Cayin N3 Ultra hiss | HiBy R6 Pro II hiss |
|---|---|---|---|---|---|---|
| Shure SE846 | 9 Ω | 0.04 mW | +32 dB | +37 dB | not published | not published |
| Campfire Audio Andromeda 2020 | 9 Ω | 4.0 mW | +12 dB | +17 dB | not published | not published |
| Audeze LCD-2 Classic | 70 Ω | 0.79 mW | +22 dB | +27 dB | not published | not published |
| Beyerdynamic DT 1990 Pro (250Ω) | 250 Ω | 0.63 mW | +17 dB | +24 dB | not published | not published |
| HiFiMAN HE400se | 25 Ω | 7.9 mW | +14 dB | +19 dB | not published | not published |
| Audio-Technica ATH-R70X | 470 Ω | 1.6 mW | +10 dB | +18 dB | not published | not published |
| Sennheiser HD 600 | 300 Ω | 6.6 mW | +6 dB | +13 dB | not published | not published |
| HiFiMAN Susvara | 60 Ω | 50 mW | +4 dB | +10 dB | not published | not published |
The HiBy R6 Pro II costs $101 more than the Cayin N3 Ultra. Out of the 567 models here, that difference buys 1 more model driven to 100 dB.
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 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: Cayin N3 Ultra and HiBy R6 Pro II.