I got here early in the afternoon on Friday and had a chance to spend some quiet time with the HD800's. I listened to the in the Headroom room with single ended termination. I borrowed one of Vicki's cd's (Lee Morgan).
It sounded very neutral and natural to me. No hyped up bass or treble. Maybe it's not one of those knock your socks off kinda sound but IMHO, that sort of thing doesn't equate into long term satisfaction.
What I was looking for was an AD2000 with bass and I think that it fills the bill. After listening to them single ended (I'll give them a listen balanced today) I'm pretty sure I'll buy a pair.