I tested the following DACs with RP1 when I had it and the difference was immediately apparent:
Chord Qutest, Mytek Brooklyn 2, Bryston BDA-3.14
I ended up with Chord Qutest.
Amp was Rogue ST100 driving Martin Logan Montis.
DACs should not be quickly A/B’d by switching inputs back and forth. You need to listen to at least the entire track and even better listen for few hours with one dac before switching to another.
If after getting acclimated to one DAC it all still sounds the same to you, you’re either not capable to hear the differences or your system is not revealing (it’s not RP1 cause it’s pretty transparent) and or your room acoustics are bad or all of the above.