The 64 Audio U6t is 9Ω at 98.0 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 U6t needs 5.0 dB more than the Volur to reach the same loudness — 1.6 mW against 0.50 mW.
| Specification | U6t | Volur |
|---|---|---|
| Impedance | 9 Ω | 6.3 Ω |
| Sensitivity | 98.0 dB/mW | 103.0 dB/mW |
| Sensitivity (voltage) | 118.5 dB/V | 125.0 dB/V |
| Power for 100 dB | 1.6 mW | 0.50 mW |
| Voltage for 100 dB | 0.12 V | 56 mV |
| Current for 100 dB | 13.3 mA | 8.9 mA |
| Highest source impedance that leaves them alone (one-eighth rule) | 1.12 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.
38 sources are low enough in output impedance for the U6t under the one-eighth rule but not for the Volur (FiiO SnowSky Tiny B, FiiO KA15, FiiO BTR15, 35 more).
8 sources stay below the audible-hiss threshold with the U6t but cross it with the Volur (FiiO BTR11, FiiO K11 R2R, Lake People G103-S Mk II, 5 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 U6t 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.