Well, I use Premiere but I’ve never used a dedicated 5.1 track, I’ve always split my source audio into mono WAVs from the beginning and edited using each one on a separate track, linked together, with each track panned left, right, or center as needed. Then I use my above method of muting all but one track and exporting individually.

Can you export as a 5.1 PCM (probably a WAV file)?

Also, just noticed the end of your post - yes, we do have the theatrical DTS audio. I don’t remember if I have it somewhere or not. Schorman is probably the one to ask for access to that.