I know, my desktop amp puts out 300mW @ 300 Ohm

whereas the Plenue D2 is somewhere around 10mW

yet, those are enough to go TOO loud on my 250Ohms Beyerdynamic DT 990

I have 250 Ohms Beyer DT 990 and they comfortably run even on my Plenue D2

I mean, there must be a lot even more demanding headphones out there, but most desktop amps also deliver a lot more power...