I was running my audio directly off my HTPC a few months ago. Had Thriller in 24bit, Brothers in Arms in 24bit, and a couple Peter Gabriel CDs in 24bit. I A/B'd them all against the 16bit cds and couldn't hear a difference at all. And I even wanted to. Same goes for my car setup which, quite honeslty, is even better than some of the store demo rooms I've heard.
FWIW, I also have a hard time distinguishing the difference between wav and 320kbps. If the system I'm demo'ing on doesn't have some dynamic headroom, it's usually a bust for me.
That's actually one of the main reasons I'm looking at going with a receiver that has over 200w per channel. A lot of the locals 'audiophiles' don't seem to understand this. *shrugs*