For what it's worth, I took part in a controlled comparison between DD and DTS verses the original 35mm magnetic master of a movie reel (Terminator II, nuclear nightmare sequence). This was done on a large mixing stage like the one where the movie was mixed originally, and the original mixers were present. At least for this reel and this movie, which had extremely soft and extremely loud sections, I could not tell any huge difference between DD and DTS, except for the fact that the DTS version was mysteriously more "hissy" than the DD version. Neither sounded totally transparent when compared to the 35 mm magnetic master, but it was actually closer than I would have thought.

The encoding of both the DD and DTS versions were done under strict supervision, so DTS couldn't do any manipulation to surround levels or bass level, as those in attendance would have picked this up immediately.