"and then you've GOT to mix it at exactly the right point so you aren't left with, for example no bass at all."
exactly. i've seen him play his usual multi-source DJ sets, and i have no idea why he'd want to play this way.
i've also seen him use a footpedal with FS/Traktor, which allowed him to tap his foot to get the tempo more accurate (thereby making adjustments while in the mix).