I have a presonus firebox and i have it hooked up to my mac pro running logic 8. When I plug in the firebox there is no audio, none of my loops have audio, but there are levels. I can record my voice, but to hear it I have to unplug my firebox. When I record in Garage Band it works fine. How can I get sound to come out of the internal speakers when my firebox is plugged in?