Just found a new source elsewhere named “Bill.and.Teds.Excellent.Adventure.1989.REMASTERED.1080p.BluRay.x264.DTS-FGT.mkv”. I used MKVToolNix to merge the video of COMPLETE and the DTS 6 channel audio, chapters, and English subtitles of the new source, and it synced perfectly!

The whole disc was just posted, but its DTS-HD codec is only 2 channel audio: Bill.and.Teds.Excellent.Adventure.1989.2160p.COMPLETE.UHD.BLURAY-COASTER

If you have the old non-remastered 720p AMIABLE version or another with the 6 channel audio, you might be able to mix the first video stream from COMPLETE (or the only video stream from this) and the audio stream from AMIABLE using MKVToolNix. I don’t know how well they sync though.

The remastered AMIABLE releases are 2 channel as is the old non-remastered 1080p AMIABLE. Not sure why the 720p of the old got 6 channel. FYI, I am basing my info on NFO files, not on first-hand knowledge. I don’t have the old files.

Thanks for pointing that out, Keith! The film only had 2 channel audio, and so this is more faithful to the original. But the DTS audio makes for a better experience, and so I am holding out for that.