I had a similar problem - trying to route BIAB and the output from Guitar Rig to Quicktime (or PhotoBooth). I can route one thing, but then nothing else works ..

Didn't / couldn't find a solution to the problem. It's either stick an external mic, route that to QT and record the lot together, or do the whole audio in GarageBand, record the video using an external mic for audio as a guide and then replace the guide audio with the GB.