Sorry, Ian
Where I mention "LSB/USB" in my previous post - substitute "LSB/MSB". I have been trying to solve a "USB" problem on an old laptop, so I guess I have that terminology stuck in my head.
Also, take a look at Jorgen's site as he suggests. He has a nice arsenal of programs that will run on your MAC. His caveat for the MIDI Revoicer is that it only detects the initial voice settings at the head of the file and ignores any subsequent changes, but at least it will give you the much needed start. From there you could do manual searches thru the event lists and just substitute whatever MIDI Revoicer used on the initial settings. I suspect that MIDI Revoicer would work just fine on the majority of MIDI files you would run thru it with no additional work.
Good luck !
Thanks, Jorgen ! and sorry I didn't send him your way to begin with.