Are there any MIDI players about for the Amiga
?
The only dedicated MIDI player I know of is GMPlay, which is freely available from the Aminet.
GMPlay consumes a fair chunk of CPU time, so prepare for some slowdown unless you're using a high spec '040 or above.
Alternatively, you can load MIDI files into Octamed Soundstudio, but you'll need to assign instruments to the notes manually and I cannot get it to play back any more than four channels.