[Update] Just found a nice article that explains things a little more clearly then I did. I still have the same conclusion, support for the new audio formats sucks.
Now that I own a PS3 I was thinking about upgrading my receiver to one that supported the new audio formats available on HD disks.
Getting the video right for HD is hard enough, most display manufactures are not exactly forthright about the real capabilities of their displays lots or marketing material will reference 1080i/p when the set can't do those formats. Audio is way more difficult, there are 7 different audio codes that HD-DVD and Blu-ray support. Dolby Digital, DTS, Dolby Digital Plus, DTS-HD High Resolution, Linear PCM, Dolby True HD, and DTS-HD Master Audio.
Andy Pennell wrote an interesting article on how audio works for HD DVD, specifically he shows how the add-on for the 360 works. The 360 player doesn't support the new audio formats directly instead the player transcodes the audio to WMA Pro, DTS, or Dolby Digital. Andy considers WMA Pro to be the best format. My current receiver supports DTS and Dolby Digital, I am currently using DTS. Reading the avsforum HD DVD audio faq was only more confusing, some of the new formats can be sent via HDMI, but only in a limited format that drops some of the audio. If you actually have a standalone player it looks like the best way is to use the analog outputs.
I could not find equivalent information on the PS3 handling of the new audio formats. There are two articles (1, 2) on engadgetHD that is complaining about lack support for True HD. I am currently using the S/PDIF out on the PS3 to run audio to my receiver, what the PS3 is doing is unknown.
This was originally going to be a list of receivers I would consider buying, but with my current playback gear, PS3 & 360 add-on it doesn't make any sense to upgrade my receiver. The HD audio formats are currently a real mess.