I assume you mean AmigaOS 4.1 Update2.
Yes, new Amiga's (PowerPC machines running OS4.x) can run OS3.x software in Emulation. It might not run everything but usually things run.
I don't know much on MIDI, but if this is on MIDI files, you can actually run them in software, and do not need hardware over RS-232 for it. I think there is a software
which plays MIDI files over AHI on os4depot.