Hey,
Regarding the mentioned Mac OS X problems, I found this:
Java for Mac OS X 10.6 Update 1 (Dec.3rd 2009) changes things in terms of JVM midi support. With this update the world's most advanced operating system does not need a third party Midi service provider like mmj for javax.sound.midi to access hardware anymore. Here is Apple's release notes, see Radar #3261490 under JavaSound.
Second: You may still want it, though
Apple's java Midi implementation appears a bit half-hearted. It does not consider MIDI data with status bytes >= 0xF0 to be valid (i.e. does not work with sysex, MIDI clock, timecode etc.), ignores timestamps on Midi events, device names will default to only the port's name (without hints on the device this port belongs to) and there may be other things missing alike.
And those mentioned issues with status bytes sound an awful lot like the problem Mac users are experiencing. So the solution may be to install this:
http://www.humatic.de/htools/mmj.htmFollow the instructions in the readme.txt inside. An alternative that seems to do the same:
http://www.mandolane.co.uk/swMandoMidi.htmlPlease try it, and let us know if it helps or not.