Stress, with the 8 out you wanna start counting your inputs of the soundcard and how much you got left... Software-wise, I got one mpc on output functioning like a midi (thru) recorder, between logic and all the other hardware devices controlled under logic. While its in thru mode it also works as the stand alone mpc but slaved to logic's tempo. Basicaly the idea is to create beats on the mpc and other hardware connected to it and save the song to a midi file ( file type-1 ), which you load back into logic again to edit the arrangements made on the mpc. When done you set the mpc to record in a new song and let it record all the midi channel's data from the logic editing you've done into the mpc. Once the song is finished, you arm the inputs you want to record the hardware that you have used and/or the 8 out from the mpc and disarm the slave mode. Once doing the tracking you can add vsts and mix the recorded audio channels. Point of doing this route is to use the timing of mpc, not the pc and have flexible editing capabilities. I also use this for arranging live stuff, basic rule is to keep all editing and scoring to midi, not audio or vst unless there's a laptop in the midi-chain, imo better use a hardware sampler(s).
The other way around is to slave a laptop to a mpc with a vst host. Basically it will support 16 chnls for the amount of midi output given by your soundcard on which you can load a vst instrument, FL is also a vst instrument. If your soundcard has rocksolid timing and enough I/O you can stream the 8 out back into FL while being a vst client under the VST host. Note that the vst host does not have a sequencer, its all mpc timing and a fast! laptop.
