To reproduce:

• Launch the game with the music mod
• Run aplaymidi -l to see the ports
• None show up (if some do show up, it'll be the same as when the game isn't running)

nobody seems to care about this T_T

I actually downloaded the source and checked what was the problem, first I've seen that the exception MidiUnavailableException was ignored in the MidiHandler.java file. So I printed the stack trace and I got this message:
javax.sound.midi.MidiUnavailableException: No transmitter available

I'll try to check the issue and solve it if possible

any solution for this?