If anyone wants to try playing MIDI on OSX I've got a new
sqMacMIDI.c file, as well as a VM compiled with the changes
(VM generated from an 3.2 (4956) image).

It seems to work on my system, which is a dual-450 G4
using a MIDISport 4x4 USB MIDI interface.  You can also
playback through virtual MIDI ports, for instance soft-synths
or ports created through apps like MIDIPatchbay.  I'm running
OSX 10.2, but 10.1.5 works too last time I checked.

The SimpleMIDIPort class works 'as is' with the
new external code.  At least I can download a fresh image
and play the ScorePlayer demo through any of the MIDI
ports or through Quicktime.  I didn't need to make any changes
to MIDIPlugin or the primitives' glue code.

I have a MultiMIDIPort class also working though the code
could use some rearranging - right now it's all class methods
(which may make sense since I can't foresee there being multiple
instances).

There are many issues (buffering, time-stamping, using
semaphores, etc) that could greatly benefit from someone
with more MIDI knowledge taking a look.  I've got things working
to the point of being able to send notes, program changes, and
control changes to any port/channel for immediate playback.
I haven't gone very far beyond that except for adding some
MIDI input data buffering (and there's probably a better way...)

Anyone brave &  patient enough to try this stuff out let me know -
I very open to suggestions and constructive criticism (or even
better: any MIDI expert who wants to take the code to the next level..)
There are definitely some rough edges and kludges - but I think a
good foothold.

Thanks,
Jay