I came across an original Passport MIDI card for $30 and figured, why not? Got it hooked up in my IIe to my MT32 pi (for anyone not familiar, that is a raspberry pi based Roland mt32 emulator) and gave the only software I know of that uses it (Ultima V) a try. Worked and sounded great.
Were there any other games that utilized MIDI at all? Or any playback software? I'm not finding anything outside of U5 in my searches.
Passport didn't include a disk with the original card -- just a manual and two MIDI cables. (I got mine at a discount because it was missing the MIDI cables!) The only other software I can remember was a a BASIC sample program in the manual.
Here's a scan of the manual, in case you don't have it. It also describes the theory behind the interface and the technical details of the circuits.
https://www.applefritter.com/files/2024/09/12/Passport%20Designs%20MIDI%20for%20Apple%20II.pdf
NB: The documentation is rudimentary and sometimes obsolete! This Passport MIDI interface pre-dates General MIDI by almost a decade, so there's lots of discussion of attaching non-MIDI equipment that already existed at that time. It doesn't seem to anticipate standalone tone generators like the MT-32, which just didn't exist yet.
Maybe this is of interest to you:
https://www.muzines.co.uk/articles/passport-midi-4-plus-and-midi-8-plus/9094
https://archive.org/details/MIDI8Plus_v12_4amCrack
http://www.apple-iigs.info/doc/fichiers/Passport%20MIDI%20-%20User%20s%20Manual.pdf