Pro Audio Support

Q:
I've tried to open a virtual instrument on a track in Garageband. Where is it in the instrument list?
 
A:
In the New Track or Track Info window, if you don't currently see Details click the triangle next to Details.

External virtual instruments will show up in the Generator pull down menu.

If you don't see a Generator pull down you're likely in a Real Instrument track and not a Software Instruments track.