I don't believe that much in so called "highend" rigs. The mid-level amps are absolutely sufficient and there are none or maximum very small differences in sound but not in costs ;) .
I compared a lot of amps (Lehmann BCL, Beyer A1, Bryston BHA-1, audio-gd, O2, etc.) and it ends up with buying an O2 because I (and some friends of mine as well) was not able to hear any significant difference but you have to gain your own experiences.
+1. I feel like for a lot for the high-end rigs, you need really expensive & transparent headphones to hear the differences if there are any. maybe you can tell the difference w/ a hd800.