The primary use of tsmuxer is to either demux files (split an MKV/MP4/etc. into its elementary video, audio, and subtitle streams) or mux them into a Blu-Ray or AVCHD folder/ISO or .m2ts file - it can’t output a muxed MKV or MP4 or whatever.
The primary use of mkvtoolnix is to either take elementary streams and mux them into an MKV file, or to take an existing muxed file (MKV/MP4/etc.) and take out/rearrange/add audio or subtitle tracks, outputting an MKV file.
Basically, mkvtoolnix will give you an MKV file at the end that contains exactly the tracks you want, but tsmuxer can’t do that (you could make it give you an m2ts file or an authored Blu-Ray with no menu, though).
Well, so far so good. mkvtoolnix seems to be playing nice with the 4K77 (4K) file, and appears to be rendering a new file with all soundtracks (except my preferred 35mm Dolby A track) ‘nixed’. Looking forward to seeing what it spits out.
Thanks again for providing me with some fun fodder, Chainsaw!