How I write MIDI files for the beast:
- Write in Sibelius (MuseScore is similar and free). You can allocate as many staves as you want to each of the ~registers: glockenspiel, octaves, counter, bourdon, and system+percussion+mannequin.
- When you’re through, File / Export / MIDI File. Select A Different Playback Device and Type 0, and set Tick Resolution to 256. Hit OK and save somewhere.
- Open that file in Anvil Studio (free). In View / Mixer, delete or erase any unneeded channels (e.g. vocals), then set the glockenspiel to channel 4, the octaves to 3, the counter to 2, all the bourdons to 1, and system, percussion and mannequin instructions to 6.
- Save using File / Export MIDI Format 0 File.
Two interesting generalist links: