Originally Posted by MIkeDuke
can you please explain what the differences are here:
"The 4K UHD also includes both a remixed and restored 5.1 DTS-HD master audio track, as well as the original 1968 6-track theatrical
audio mix (formatted for 5.1 DTS-HD master audio)."
The way I'm understanding this is that there is one DTS-HD MA track that has been remixed and restored, and one DTS-HD MA track that has been created from the original 1968 6-track theatrical audio mix, making a total of 2 audio options.
Remixed possibly means that a new final mix has been rebuilt from original audio stems or sources (such as separate tapes of dialog, music, and sound effects) assuming they were available. There has probably been some optimization of the mix for the home theater environment, such as having two surround channels rather than one, and having an LFE channel available. Restored probably means that there was some work done to clean up the sound and remove noise and distortion.
I believe the original 1968 6-track theatrical audio mix (for 70mm) would have been Todd-AO format with 5 behind the screen channels and 1 surround channel. To format this for 5.1 DTS-HD MA playback in the home, the five behind the screen tracks of the source have to be mixed down to three front tracks, and the single surround track of the source copied to both surround tracks. There was no LFE track on the 6-track as a source for the DTS .1 channel, so there's really no need to use it at all. However it's possible that some of the lower frequency content from the 6 channels was filtered from them and used to create an LFE track. That doesn't really accomplish anything for anyone who has a playback system with bass management as it would do the same thing. Ultimately that makes this 4.0 audio in a 5.1 format.
It looks like there may also have been an original 4-track theatrical audio mix (for 35mm). If so it may have been a mix-down from the 6-track, or it may have been a completely independent creation. I don't think creating independent mixes for different audio formats was unusual at the time, but I'm not sure if it was done with 2001.