Midi Books This site deals mainly with religious music. Click on the site index and scroll down to MIDI Sequencing for Musicians. Click on that and some nice book titles will come up. I have the MIDI Book and it's a good starting point.
Tom Scarff Here's a source of electronic music components. Tom sells MIDI circuit boards for both diatonic and piano accordions. There's a lot of musical theory, including a page on the various systems for tuning musical scales.