Official comment
You can't record a mix from the IF2, you need to record the output from your mixer. The IF2 only provides control tone from the turntables into the software, then the audio output from the individual channel to pass to the mixer. The mixer itself is where the magic happens, so if you want to record a set, it has to be post-master. And if you're needing an IF2 box, then chances are your mixer doesn't have a built-in audio interface.
I'll recommend using an external recorder, or running the output to another audio interface to record from that.