You would think the mapping would match GB. The first thing someone is going to do with IRB is export to GB when using the OS X version so they can record themselves with an IRB backing track. I thought General Midi was supposed take care of this kind of interoperability.
This kind of thing is...
I tried exporting a song in midi format and importing it into Garage Band so I can record a part and ran into some problems with the drum track. I was exporting the song Blue In Green, which is a 60bpm track with brushes and very little going on in the drum track. I dragged the midi file into GB...