The specs page for that hardware (Moog Minitaur) doesn't claim that it can transmit audio over USB, only that it has USB MIDI- essentially it has a built in MIDI interface.
If you wanted to get audio from it into your computer you would have to connect it to your computer's line or mic input, or an external soundcard - which may itself connect via USB. One way to handle audio in OSX would be Core Audio. You shouldn't need to write any drivers or anything to deal with the low-level I/O with the soundcard, as the soundcard should come with a driver if there isn't one already in the OS.