Dolby TrueHD, DTS-HD High Resolution or DTS-HD Master Audio soundtracks are only available on some HD-DVD or BluRay discs. Due to the size in gigabytes needed to store the data in these new audio formats they are not available on regular DVD's. It's just not possible to derive Dolby TrueHD or DTS-HD from the DD or DTS of a regular DVD no matter what connection you use.
If you have an HD-DVD player or BluRay player with internal decoding and with 5.1 or 7.1 analog outputs you can still enjoy these new formats without HDMI - as long as your receiver has 5.1 or 7.1 analog inputs.
If you're watching only regular DVD's then there's no need to worry about audio thru HDMI since the soundtracks on regular DVD's are carried on optical or digital coax without limitations. For regular DVD's HDMI becomes a factor only when you're dealing with upconversion to 720p or 1080i/p. For audio it's really a non-factor.
For more info read our discussion here and visit the links posted by diabolos:
