How do you have everything hooked up, in terms of using the SP as an effects processor?

i don't know if you've searched, or if it works but i've said a few times. i set up the assignable outs and then use input thru from the rec in. ideal set up for my personal work flow. if you need any more details jus shout, safe.

sometimes i just put the sp outs into the mpc in and just resample stuffinto my mpc.

or i use a midi cabel, midi in in to the sp midi out A from the mpc.
and there it stps for my i only can play a sequence on the mpc and play one sample from the sp with it.(sorry for my bad english)

Can you elaborate a bit on your actual cable connections? You aren't using an external mixer right?

ok, here we go...

mpc main outs to your recorder/daw/mixer
mpc assignable outs (1/2 to make it stereo/in pgm mode) to sp in's.
sp outs to mpc rec in (you will have to turn input thru on in mixer mode).

This way you get no feedback loop and can resample anything from the mp with sp effects instantly, no need to touch any wires. In my opinion, it is the best way to use the 2 together.