I think burn in helps it sound a bit less dark. [...]
Let us know if you have heard them out of speaker amps as they seem very efficient already and not sure how much more performance one can get. They run amazing well on my Dave + Farad3 setup.
Oh, I got mine used so is already well-worn-in.
It actually sounds great of the the speaker amp (Pass Labs X150.8, 150 watts), which I tried for the first time for about an hour the other day. I have more of a usable range with the pre-amp's volume knob than I was expecting (The amp has 26dB of gain, which is pretty much the typical amount of gain for an amp of its power class).
There's no change in tonality, which is good in the sense that sometimes speaker amps will mess with a headphone's tonality in unexpected (undesired) ways.
Tonality aside, the X150.8 imparts a similar character to anything that I plug into it, such that the first time I tried it, my immediate thought was that -- strange as it is to say -- it reminded me of the Utopia. Extra dynamic ("explosive" is the word that comes to mind). And the soundstage is extra grand and open with anything with a lot of air and reverb and stuff.
The heat of this amp is no fun in the middle of the summer though, lol. But I imagine I will use the Sollitaire P much more with it once it cools down at least a few degrees