Maybe I got you wrong now, but I have a certain suspicion you are now only concentrating for impedance / numbers as if this is the most important thing to look for when buying phones.

If your phones output is powerful enough (applicable to most RME recording interfaces) then the impedance of your phones is not so important, but I would avoid getting phones with a higher impedance than 250 Ohm.
If you have powerful phones outputs like with UFX II, UFX+ and esp ADI-2 DAC and ADI-2 Pro, then impedance is not really an issue.

Not only the impedance has an impact of the final volume but also how efficient the drivers are in the phone. So I would not be too religious when looking to the impedance values. Its one of several things that need to fit. Most important is that phones are suitable for the intended purpose, comfortably or that you are able to work with them. Be it for recording vocals, mixing, EQing, mastering ...

If you want to use your phones with smartphones, then look for an impedance of under 20 or 30 Ohm. But .. we are not a smartphone forum here ... aren't we ..

So I would focus more on features that are primarily important to you:
- do you need open or closed phones (if you are vocalist and do not want to record portions of the backing track -> closed)
- do you need more a HiFi alike sound or is the more for studio work
- do you like the "sound" or can you use these phones to work with EQs in the DAW
- are the phones comfortably to wear
- is the cable long enough and replaceable ...

And somewhere at the end of the list comes .. and is it by occasion loud enough ?!

And if you got already a nice RME recording interface and if the impedence is not very high, well then you found a nice match.

You can use this excel to check the power of some RME phones preamps, to have a little comparison:
https://www.tonstudio-forum.de/index.ph … 0-08-xlsx/
But not all products (and also not ADI-2 Pro/DAC) are included here, only USB/FW/TB interfaces.

And maybe check out what professional mastering engineers are looking for when testing studio phones:
https://recording.de/magazin/vergleichs … oert.2621/
If German is not one of your languages .. use a translator, google or deepl.com.

Thanks all for your answers.
Unfortunately I am in a small island and no big music stores here to test and chose.
So I am forced to make my choice collecting opinions and reviews.
Ramses, I read articles you posted, very helpful, thanks.

My short list until now is.

Beyer dt770pro
Sennheiser hd600
Ollo s4x
Akg k702

Will appreciate your opinion on which of them will give better results in cooperation with my interface, ff802 in term of power and low distortion.

Thanks