superbit? What is it?

I guess I can comment on the audio.

I can really only comment on The Fifth Element, as it's the only disc I've seen enough to know the soundtrack well enough.

The DD track is slightly better than the old version. There's a bit more detail to it than old version had as the old DD track was compressed more than the Superbit version is.

I didn't care for the DTS mix on it though. You can argure all you want as to which is better DTS or DD. It's more about the mix, than it is about the compression scheme. I usually preffer a DTS track. Though sometimes the difference is non-existant. And sometimes the DD track is better, as I feel it is on the Superbit Fifth Element.

Though if you really want the best audio track, go with the LD release.

I was under the impression that Dolby Digital and DTS had fixed compression rates (unlike, say, MP3s). In that case, the soundtrack on both standard and superbit DVDs would be identical unless the studio went to the trouble of remastering--and why would they do that?

Both DD & DTS have 2 standard bitrates. On Superbit DVD's the higher rate DD is used, and the lowed bitrate DTS is used. If the full bitrate DTS is used they have no room for a DD track. The early DTS titles had no DD track on them, as they were full bitrate. Which meant there were two different releases, the DTS version, & the DD version. I believe the last full bitrate DTS DVD was Saving Private Ryan.