I want to have MIDI support on MMOS2, because I want to try to get MIDI sound on solo old OS/2 games like Lemmings, Makman.
The Makman MIDI files seems to require more instruments than supported by Timidity by default, if
https://onlinesequencer.net is anything to go by. So you may need real, supported hardware after all.
You could try to convert (directly or indirectly) a sound file to a supported MMOS/2 file format, e.g. WAV, and next hope that Makman uses the right technology. For example, you can copy Makman's EATING.WAV to EATING.MID, and use
x:\MMOS2\PLAY.CMD FILE="EATING.MID" to play the renamed file. Of course it'll be a WAV file, but with a file name expected by the app. If that works with Makman, then...
COPY VEMBO.MID VEMBO.MID.BAK
Somehow play VEMBO.MID and record that as VEMBO.WAV (or convert an unsupported file format binary, if possible)
Rename VEMBO.WAV to VEMBO.MID
If.
To test, please first try this with an existing audio file, per app, and make sure the sound file will actually be used by the app. I don't know how to let Makman play VEMBO.MID, without having tested that. I cannot hear a MP3 files saved as VEMBO.MID, but that doesn't rule out that this won't work with Makman.