Ok quick update. This is interesting. On the disc 300, if I change the audio setting to DD TrueHD, it sounds a heck of alot better. It's weaker on just 5.1 (plus?), the default.
Go to another HDDVD, Mission Impossible III, the only option is DD plus, and it's obviously weaker on my AV receiver. Not sure what's up with that. Anyone else think the MI:III is a weaker than normal sounds disc?