I have never heard DD+ or TrueHD because I don't have an HDMI receiver...But, my Toshiba HD-A2 down-mixes these codecs to DTS 1.5mbps and I can tell a difference in how it sounds. Fuller, smoother, and richer.
The movies I've seen since buying my HD player that have fantastic audio tracks:
-Serenity
-Training Day
-The Ant Bully
-Van Helsing
Not as good:
-Corpse Bride(was a little better than standard dolby digital)
With HD DVD, all you need is a HDMI 1.1 receiver to get DD+ and TrueHD. Or a receiver with analog inputs/paired with a dvd player with analog outputs.
