The 64 Audio Nio is 6Ω at 105.0 dB/mW; the 64 Audio Volur is 6.3Ω at 103.0 dB/mW. This page is only about what they ask of an amplifier — not how they sound, which no specification on either sheet can tell you.
The Volur needs 2.0 dB more than the Nio to reach the same loudness — 0.50 mW against 0.32 mW.
| Specification | Nio | Volur |
|---|---|---|
| Impedance | 6 Ω | 6.3 Ω |
| Sensitivity | 105.0 dB/mW | 103.0 dB/mW |
| Sensitivity (voltage) | 127.2 dB/V | 125.0 dB/V |
| Power for 100 dB | 0.32 mW | 0.50 mW |
| Voltage for 100 dB | 44 mV | 56 mV |
| Current for 100 dB | 7.3 mA | 8.9 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 0.75 Ω | 0.79 Ω |
| Sources that reach 100 dB out of 280 | 280 | 280 |
Every source in the database that drives one of them drives the other. On power, the choice between these two changes nothing about what amplifier you need.
7 sources stay below the audible-hiss threshold with the Volur but cross it with the Nio (Grace Design m900, FiiO M33 R2R, FiiO K17, 4 more).
280 of the 280 sources here reach 100 dB on both. That count is about power only — the output-impedance and hiss lines above are separate questions, and a source can pass this one and fail those.
Each model has a page of its own with the full source list, the hiss estimate and the provenance of every figure above: 64 Audio Nio and 64 Audio Volur. Every figure on this page comes from what 64 Audio published, or is derived from it — what that maker publishes, counted.