Matt, thanks for the welcome and the response. Taking things a step at a time. Having once imported the multichannel files with the custom fields into my Mac MC (and having deleted them from the library) I now see that those fields are appearing in the tag list viewer (at lower left). Is that what you mean by "creating the tags" on that side? Do I assume the Mac MC library now knows about those fields forever? When I re-import a custom-tagged multichannel file the custom field values are still empty. Is it possible that when I earlier imported the multichannel file, and MC didn't recognize all the fields, it would have discarded the values from the unrecognized fields in the original multichannel file itself? (Surely not?) Is there a way to "create a tag field" without a file selected so that the library will be ready to receive a custom-tagged file? If so please point me to it.
I've also experienced MC reporting other "failures" on some but not all tracks when doing the "re-rip" swap and tag update. The stereo versions start without the two custom fields, so there are fewer fields. On some tracks data from two fields seems to have been merged into one (in fields unrelated to the custom ones), and in others not. Are you saying that I have to predefine the custom fields on the stereo files *before* I can "re-rip" and swap them out for the multichannel ones and update tags to pull the tags accurately from the multichannel ones in the library? If so, can I do this in batches and simply add the two custom fields to, say, 50 albums worth of files at a time without populating them with values, then delete them from the library, and then the "re-rip" and update method (importing the multichannel files, deleting them from library, replacing them with the stereo files in the original directory, and updating tags both directions) should work correctly?
If I import both the multichannel dsf and the stereo dsf of the same album into the library (I'm only using the one main library so far), they get combined so that I see duplicate tracks listed under the same album heading, so clearly I can't allow two versions of the same album in the same library.
I looked at the spec for dsf and it allows frames for ID3v2 tags and your notes say MC Mac is at ID3v2.4, which I see allows user-defined tag fields, but doesn't talk about user overwriting of producer-supplied values. Are we confident that if I've overwritten the producer-supplied value for a tag field in the original multichannel file, and then do the "re-rip" swap for the stereo version, and *if the field labels are equal in number and identical in spelling* in both files, that the multichannel values first entered in the library will always overwrite any producer-supplied values that were in the stereo files? In my tests it seems to happen most of the time but not in all fields, but that may be because of the discrepancy in numbers of fields between the two versions in my initial tests.
Finally (thanks for your patience), I'm concerned that my MC library database is now quite confused (as I may be). Is there a command to wipe it out so I can be confident that, following the instructions you are kind enough to be providing, I'm starting from a clean state? If I have to import the stereo files to add the two custom fields, I'd want to erase any of their producer-supplied values from the MC library prior to starting the "re-rip" swap process. I want the tags from the multichannel versions to be what MC remembers so it can update the stereo versions with those values.
Many, many thanks.