I'm not sure how your software works, but with ScreenFlow there are two audio sources and two video sources. For audio I record the built in mic and the computer audio (Reason). For video I record the built in camera and the screen. Later I record the VO track based on editing and re-recording what I recorded on the built in mic.
But if you want it all in one go, plug your mic into Reason and monitor that audio track, then you only have to record is what comes out of Reason. :-)
Giles Reaves, aka 'selig'
Audio Illusionist, Musical Technologist
Selig Audio, LLC