When I connect my microphones and headphones in through my M-Audio interface I expect these should override the mic & speakers that are built into my MacBook Pro - but that's not happening. Instead: 1) the M-Audio interface DOES NOT provide signal to my headphones as I record, 2) the speaker/headphone jack on the computer DOES provide signal to my headphones, 3) and the built-in speakers play as I record. Also: 1) the M-Audio interface DOES show the clip and signal lights reacting to my pro microphones, 2) however, the system records signal even if I turn the mic volume to zero on the M-Audio interface. This makes me think the built-in mic is also recording, or perhaps is the only thing recording. Lastly, when I attempt to overdub on a new track, sound from the built-in speakers can be heard, which again is picked up as I record and presenting me with two monitoring signals that are out of sync - the speakers and the headphones. Sorry for the lengthy message. Any suggestions? Thx.