XMI stands for eXtended MIdi. Each .XMI file can contain several tracks, and the first track in the gfay file you mention sounds like the ButcherBlock music (I think the track you're looking for is track 5, off the top of my head).
Extended MIDI was created by a single company around ten or fifteen years ago, and the format is particularly obscure. It supposedly does some things that MIDI doesn't do, but it doesn't support variable tempo (even though .XMI files can contain the "set tempo" command, players must ignore that command when playing .XMI files). Exult, an open-source rewrite of Ultima VII (available here:
http://exult.sourceforge.net/) is the only place where I was ever able to find out how to play them. I've actually written a small .XMI player using it. XMI files are otherwise closely related to standard MIDI, and the Exult code handles both file formats (I didn't bother implementing the standard MIDI stuff for my player, but it wouldn't take much to add it from the Exult source).
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