as New Homebrew said, DTS is lossy compression. it's akin (but NOT the same thing) as a 5.1 surround sound AC3 encoding. again, it's a different compression scheme involved (still lossy), with surround sound.

haven't you people ever looked at the Audio setup/options on official Hollywood DVDs? many of them will have 2 versions of AC3 audio (2.0/Stereo and 5.1/surround) along with a DTS surround track. i'm not trying to be mean, at all. i figured most people had some idea of the DTS format.

for more info, check out...

http://www.dtsonline.com/entertainment/surround/