I'am having problems with MIDI on Logic.
It keeps coming up with an message saying: Can't find Mac OSX midi and another message comes up when it loads saying: Midi (0) can't be found,please check other programmes to see if its being used.
You mentioned Mac OS X briefly. What version are you using?
If anything, head to Applications-->Utilities and check the MIDI setup icon there. You might be able to configure what you need there.
I had to do this in order to get my MIDI gear working on my iMac G5. I also had to install the software for my USB MidiSport 2x2 to be supported under Mac OS X. Make sure you don't need any extra software for your MIDI interfaces to be recognized by the Mac. For example, my MidiSport loads the firmware through USB every time so that it works. This is why I can't ever get it to work under Linux...it shows the lights working thanks to the usb-audio support but no MIDI data is processed because M-AUDIO hasn't provided the necesary software to push down the firmware to it.