Check the disc or the back of the cd case. A lot of them are HDCD but they don't advertise it in big letters cause it is now old technology. Joni Mitchell's cds were "rereleased" as hdcd, and a lot of other cds. Pet Sounds by the Beach Boys sounded pretty darn good on HDCD.

See http://www.hdcd.com/music_catalog/welcome.asp

M22s, QS4s, M2 center, Hsu stf-1.