Finally I think I have my iTunes working on the iMac. By following Apple’s recommended procedure, it should have been simple - but I ended up with corrupt Korean ID3 tags (artist, song name, album, etc).

I’ve heard of others who have had the same problem with Japanese tags becoming garbage, and Chinese, and Thai. It seems to be related to unicode and tag encoding. Since I couldn’t find a single webpage which had a solution that worked, so here’s the procedure I followed to fix things. Hope it helps someone else someday.