To bring you up to speed, here was my initial problem:
If I dump them straight on the memory card then TF3D music tab says "No Music Found", if I sync them over WMP11 to the device then it shows them - but no album art and their durations are all zero seconds. WMP won't play them either. They're just in MP3 format and play fine everywhere else.
Then I've managed to get this far:
So, I find that I can add WMA files without a problem. So at least I have a viable work-around for the problem. This doesn't actually help me sort out what the problem regarding mp3s actually is, and I'd rather not convert 47GB of music to WMA.
I thought it may be something to do with the File Associations, that I broke them somehow by installing Coreplayer, but I'm less sure now that a Hard Reset didn't solve the problem. It still could be, I see others have had similar problems relating to the registry (although their problems always came after installation of a different media player, rather than on the devices stock ROM). Does anyone know where the pertinent registry values are, and what they should be? Or perhaps others have some different solutions?
Its a little beyond me on my second day as a WinMo user!