In the comments for a2midi.c, it says that Yamaha's card is on of the apple 2 cards. "Apple II 6850 MIDI card, as made by Passport, Yamaha, and others."

So let's try the RittorMusic Midi/4 sequencer, which is supposed to work with the Yamaha Music Interface.

./mame64 apple2p -sl2 midi -verbose -flop1 ../../RittorMusic\ MIDI4\ Sequencer\ -\ Side\ 1.dsk -debug -midiout "Portable Grand MIDI 1" -midiin "Portable Grand MIDI 1"

This looks very familiar:

[Linked Image from][Linked Image from]

but it seems to hit different addresses to get the midi data, so it just freezes if you try to play or record.

Interestingly, with the Passport Midi Mastertracks, the midi card is accessed through interrupts, and you can watch the data getting put into memory at $800-8ff (circular buffer), even after the software has frozen up. It seems to store the song data at $3000.