Both are dongles, $499 against $449. 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 Cayin RU9 reaches 100 dB on 563 of the 567 models here, the Luxury & Precision W4 on 561.
| Specification | Cayin RU9 | Luxury & Precision W4 |
|---|---|---|
| Power into 32Ω | 160 mW | 110 mW |
| Power into 150Ω | 34 mW | 23 mW |
| Power into 300Ω | 17 mW | 12 mW |
| Power into 600Ω | 8.5 mW | 5.9 mW |
| Output impedance | 0.5 Ω | not published |
| Output noise | not published | not published |
| Price | $499 | $449 |
| Headphones it reaches 100 dB on out of 567 | 563 | 561 |
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.
2 headphones reach 100 dB on the Cayin RU9 but not on the Luxury & Precision W4 — Moondrop COSMO, Symphonium Zenith.
561 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: Cayin RU9 and Luxury & Precision W4. Or put either against your own headphones in the source comparison tool.