Thanks for all the replies.
I think I must be missing something.
It is a DVD-Audio.
When I use DVD-Audio Extractor, it reports MLP (48kHz 24bit 6 channel). (See first attached photo).
When I use DVD-Audio Extractor, and select anything other than Direct Stream Demux (which yields MLP files), I do not have an option for the original 5.1 audio, ONLY mono or stereo. It does not seem to support for than two channels in any conversion.
When I tried MC convert function, MC reports "No tracks to format". See the second attach screen clip). All the files are vob and bup, etc. I don't know which to select, but when I double click on the icon that MC shows me, it plays.
The third clip displays what MC sees when I point it at the virtual ROM drive.
I'm fairly ignorant of all the different formats, so I have no idea about a DTS stream, but I don't see any DTS files.
I tried AudioMuxer but it doesn't understand vob, bup etc files, nor does it list MLPs in the file formats it knows.
I tried MakeMKV and it went ahead and made an MKV that plays. I have not tagged it as audio yet, so I don't know if all the channels came through or not.
Will report back.