I have found that, when watching a new DVD for the first time, it is well worth trying all of the available soundtracks. Sometimes one will sound noticeably better than the others (and it is not consistent which it will be in a given case.)
As an example, my live Yes DVD has Dolby stereo, Dolby Digital 5.1, and DTS. It turns out that the sound is much clearer and more detailed in Dolby stereo. Even stranger, it is also louder in that format (I had to turn down the volume after selecting it, in fact.)