When I first got my STS in October of 07, I tried out a couple of standard video DVDs to see if the player is Dolby 5.1 capable. I found that with normal video DVD the player recognizes the Dolby 5.1 encoding fine and plays it as it was intended. However, I had no luck with playing my DVD-Audio DVDs in surround mode. I tried my REM "Out of Time" DVD-A, could only get it to play 2 channel (and simulated "Center Point" Surround). I mostly listen to XM or my ipod so forgot about the whole DVD-A issue.
I did some research and found this old post -
Turns out some DVD-A's don't encode the surround tracks by default in Group 1. The trick is to use "Search" and switch to a different group. In the case of the REM DVD, the surround track was in Group 3. Once that is activated it shows the Dolby icon on the screen and plays in glorious multi-channel sound. The sound quality is very impressive.
I do have another DVD-A of Vivaldi's Four Seasons which has both Dolby 5.1 and DTS encoded on it. However, I cannot get the STS to run either of these surround tracks - there are no other Groups on this DVD besides Group 1.
When I go to the main menu on the DVD I get a message saying something like "Play this DVD-A as a DVD Video to enable surround sound". I could do this on my DVD player at home (and activate DD and DTS), but I can't find any options on the STS DVD player to achieve this. Anybody know a way to trick the DVD player to play a DVD-A as if it were a DVD Video ?
So in summary - not all DVD-Audios are created equal. If your DVD-Audio is playing in 2 channel mode (it shows "LPCM" on the screen) try the "Search" and change to a different Group - most likely Group 2. That will, in many cases, activate DD or DTS.