I generally do all the tagging and gain adjustment at rip time, so external tags are a non-problem. Ditto for song ratings and play history...I've been described as OCD, but I've never bothered to keep track of my music at that level. (Forgetting that I already own a particular CD when I'm looking at it on Amazon is a completely separate problem.
)
Actually the only thing I care about keeping in sync is the playlists. As it turns out, keeping them with the rest of the music files (i.e.
one copy) is trivially easy. You seem to be reading more into this than is really there.
At this point, I've got my questions answered and have MB working like I want it to.