Heh. Rack mount, bought it new uh... 12 years ago? 13? Back when I, you know, actually played... :} (Haven't even plugged in the keyboard in 2 years. Lookin' ta change that.) Put it this way, the last time I set this up, I was using a PowerBook 5300 and a serial port adapter.
Anyway, yeah, that's one reason I'd like audio to GarageBand, but I figure, worst case, I can use the 2 1/4" L/R plugs out of the keyboard and adapt them all the way down to a 3.5mm stereo plug to put in the line in/mic port.
So yes, I'd want:
Controller -MIDI-> K2000
Controller -MIDI-> GarageBand
GarageBand -MIDI-> K2000
GarageBand -MIDI-> Controller
K2000 -audio-> GarageBand
Controller -audio-> GarageBand
See? I don't want much...
I figure I can use either the Yamaha or GB to drive the K2000, and GB to drive the Yamaha, and the audio from both units back into GB... woot!