my gear:
-mpc 1000
-sp303
-mackie u420 (has main outputs + stereo aux output)
-ableton live

basically what i want to do is, play and sequence everything like normal on the MPC 1000, chops, drums..everything. once i have everything sequenced the way i want inside the MPC, I want to record my sounds 1-by-1 from the MPC into Ableton onto their own channel (kicks on tr1, snares on tr2, bass on tr3, etc.)

BUT

before any of the sounds actually hit Ableton, I would like for the Sp 303 to pick up the sounds, so that I can add FX on the fly, and then have the wet signals be recorded into Ableton.

would this be the correct setup?:

-mackie aux outputs -> sp 303 inputs
-turn on ext source on the sp 303
-sp 303 outputs -> mackie channel 3 inputs

how would i keep from hearing the signal twice? (once from the main outs of the mpc playing on channel 2 and the other from the sp 303 returning to channel 3)

Are you looking to record both the wet and dry signals?

If not, and you just want the wet signal, why don't you just plug the mpc out straight into the Sp in and then the SP out into your audio interface?

fot the title (send/return thing) check page 62 on the manual, well explained + cool graphic example