I’m a little late to the discussion, though I agree with TWB, Pass Labs is excellent, i have the XA 160.8 with XP 30 pre.
I was prejudiced against tubes for quite a while, I never heard a tube amp (Headphone specific amps mostly) that i liked. Over the last few years i have enjoyed some tube amps. I really would like to hear an Atma-Sphere amp in my system, though I think I will still prefer the Pass sound.