Originally Posted by Anitarf
Although I'm not sure how it chooses which sound bank to use, is that written in the MIDI file?
No, MIDIs don't contain any soundbank information. In Windows they go straight to GM.dls, other players I guess might use different custom soundbanks. In WC3 it's most likely done by either one bank per tileset, or a something to bank mapping in a SLK file. I seem to recall there are very few banks, so I'd put my money on a SLK being involved.