iMovie with Audio USB Interface

Hello.

I am using iMovie for recording audio during a Lecture (I nees to see video during recording) with a M-Audio M-Track interface (two XLR microphone).

The thing is that I can only record first microhone, because I can-t select the interface BUS on iMovie (or I didn't see it).

I also tested record with a XENYX UFX1204 (12 inputs), but I can only record from first input to.

Can anybody please help me?

Grateful