That's a bummer. I'm sure MIDI instruments are a pain to deal with.

It might be worth seeking out a backing track that's already made. I have yet to find one that wasn't labeled as to what key it was in. As far as the chords that are used, if it's a blues progression, knowing the key is enough. If it's another type of progression, it's a worthwhile execise to figure out what chords are being used.

Backing tracks are generally simple since their purpose is to give you something to solo over, not to write a great song. Some of them do sound really cool though.