Yes, using the RS232 on the Minimig, I tried it briefly - the MIDI interface I used (TRD?) originally pulled 12V (I think, sounds weird...) power from the 25 pin Amiga serial port, and since the serial port on the Minimig is only the usual 9 pin one, I used a PC PSU to feed both the Minimig (5V) and the MIDI interface. There are others that have found more convenient ways though, one guy even made a MIDI-board that would fit inside the typical Minimig case.