sell the djm400 before its worthless and get yourself a midicontroller imo.

but to answer, booth/rec out from mixer into line in on the audio4? although i dont think traktor lets u record internally when you use an external mixer.
i'd just hook a recorder of some sort up to the mixer.

If I remember right (from our Ghetto timecode research - which, by the way is working fucking beautifully) the only way to do it is by using an output from your mixer in to the built in line input on your mac or PC.

The Audio DJ 4 is only 4 in 4 out so no extra inputs if you want to record.

Hmmmmm, I wonder if soundflower or audiojack could do it?