assignable outs will save alot of headaches.
this is only for tracking out, when you record all the individual sounds onto your pc for tweaking, mixing, arranging and mastering.
honestly, i don't think it would save a big headache. it'd take 1/2 as long to record all yoru tracks, sure, but the sound quality is less pristine.
i record 2 sounds at a time via spdif by panning 1 way left, the other way right. ie kick/snare in one recording pass. and remember, i usually use a TON of tracks on my mpc, so the entire tracking process could easily take me an hour or so. but it's no big deal. put on some ramen, put on chapelle show or something funny and just walk back and forth. you don't have to be right there when tracking with spdif cuz you don't have to worry about eqing or anything like that. yet.
my advice is to moniter your mpc sound via spdif, track via spdif, and save the assignable outs/main outs for live use.