- Downloaded the free basic MIDI player Mighty MIDI
- Opened Audio MIDI Setup (in Applications:Utilities) and set IAC Driver to "Device is online"
- Set Playback device in Mighty MIDI to IAC Bus 1
- Opened a previously recorded MIDI file in Mighty MIDI
- Opened Mighty MIDI track list and deselected all but one track
- Started a new song in GarageBand and hit Record
- Switched to Mighty MIDI and hit Play
- Created new tracks in GarageBand and repeated record/play sequence, selecting a different track each time in Mighty MIDI
This technique will make it a lot easier to get my existing songs into GarageBand. Before, I had to open them in a notation program, carefully position the windows so that I could see both that program and GarageBand, and play the song to a metronome beat on my attached MIDI keyboard, one track at a time. I still don't think I can export MIDI, but importing it is a great help.
Now, if I could just figure out why my audio out vanishes nearly every time my Mac goes to sleep, I'd be a happy camper.