have not had a chance to try this, but I didn't remember seeing this as an option in the capture settings...

I want to record a subject off the front stero mic of my XL2, but I also want to have the subject mic'ed with a lav mic on Channel 3 (mono), would I then be able to capture both Channels 1/2 (stereo as well as channel 3 (mono) in one pass or would I have to capture channels 1/2 with video and then re capture channel 3 no video?

( I am using FCP Studio)

Liquid captures 4 channels at once. So far as I know it and another program which was mostly hardware based were the only ones.