Yep, I’ve seen his measurements. That’s the kind of specs you’d expect to see in the technical documentation of such a product.
Regardless, unfortunately his testing so far is limited to lower end interfaces mostly, so he’s only tested the UR22C. And that’s a bus powered device with a different headphone amp, rated for 15mW@40R (=0.775Vrms or 0dBu) according to the manual.
That’s an abysmally poor specification obviously and I have no clue why they bothered writing it down. Good news is according to Julian’s measurements the device more or less maintains 15mW up to 300R, topping at around 2Vrms at 600Ohms. Not great, but better than the 0.775Vrms in the specs; at least it can match a cheap phone. If you disregard the ridiculous 90ohm output impedance that is.
The wall powered interfaces, UR44C and UR816C on the other hand are rated for 100mW@40R in the manual, which is already 2Vrms and almost decent for 40ohms. As to what happens past 40R, apparently nobody knows? Anybody from Steinberg wanna tell us the voltage limit?