I spent a couple of hours listening time last night, Zune 30 with predominantly 192kbps WMA rips.
I said this in an earlier post, and I'll say it again, this thing has some really nice detail and separation. I'd go so far as to say it is a "crisp" sounding amp, not really warm, but certainly with a nice bit of low mid and bass. I do not have any particularly current-starved headphones, unless you count de-podded (w/33ohm resistors) IM716's, but this had no trouble driving any phone I threw at it, including SR60's, KSC75's, PortaPro's, the 716's, and various other IEM's. Gobs of power for my purposes, so far.
I don't love the gain switch, but it is relatively docile in terms of how it colors the sound, which I do like. It is just that, a gain switch.