I have hooked up to all 3...
And as for the audio midi? Well I'll start with the inherit problem here: If you want to modify sound, you would imagine that you would modify it thru sound in system preferences, right? WRONG! At least when Apple is concerned, because Apple apparantly loves to make things difficult as hell if they don't expect that lots of people would want to use something (And who would actually want 5.1 sound with hd movies in itunes right?
Instead of messing with sound, you click on applications/utilities/audio midi setup, and then this pops up:
Then you set your audio for 6 ch (5.1). If you didn't know about midi audio, you'd be lost for a long time like I originally was!
The problem is, it works in audio midi, but not in games like tf2. Does the OSX version of TF2 work for 5.1? I cannot seem to find this online, but it should, it's pretty much the same exact game!