not a bad idea, but I personally don't think a patchbay is necessary in this case...a patchbay, is more for when you have a ton of shit you need to all route together, but you've got a very modest set up there, and i think a patchbay would be mostly empty.
you can create an 'aggregate device' within OS X that contains all your ins/outs, and then route accordingly in logic. two other programs I would get would be soundflower (creates virtual audio ins/outs) and soundsource (allows you to easily re-route audio with a drop down in the top of your computer.
http://support.apple.com/kb/HT1215 <- how to make an aggregate device
http://code.google.com/p/soundflower/downloads/list <- soundflower download
http://www.rogueamoeba.com/freebies/ <- sound source download
close all audio apps, and install all that software first.
here's what i'd do, broken down into functional sections...
to play audio from your computer (logic / itunes):motu to your computer, as you've got it.
motu main outs to your rokits, as you've got it.
so far, you can now play audio in logic and play audio from your computer, and if it's routed to the correct outputs (motu main), you will hear it on your speakers.
to sample your turntable:numark -> pre-amp -> motu inputs 1/2....i dont know what numark table you have, but normally you need a phono preamp for a turntable. if this is a usb turntable, things will be very different.
motu outs 3/4 to your mpc ins (this will be your 'sampling' send - anything you want to sample needs to go to outs 3/4).
mpc outs to inputs 3/4 on your motu.
now, to sample your turntable, set up a track in logic receiving on motu ins 1/2. set that track to output to motu main outs, we'll call this turntable track.
create another track, receiving on motu ins 3/4. set output to motu main outs. we'll call this MPC track.
now to set up your sampling send, create a pre-fader send on turntable track to bus 1.
make bus 1 stereo, and set the output to motu outs 3/4.
so to sample from your turntable, first record enable / input monitor the turntable track. make sure you can hear the turntable. great, now MUTE that output, and turn up the send to 0.
now, record enable / input monitor your mpc track. put the mpc into sampling mode, and now you should hear the turntable -> motu in 1/2 -> logic bus 1 -> motu outs 3/4 -> mpc record in -> mpc main outs -> motu ins 3/4 -> logic -> motu main outs -> krks.
there will probably be a bit of latency, so consider starting sampling early, or configure a more complex hardware monitoring scheme via the motu (you're on your own on that).
to sample your computer (itunes/youtube)this is where sound source and sound flower come in handy.
first, run sound source. now, in the top right of your screen, the headphones icon, here, you can set your first output to soundflower (2ch), motu, or internal speakers. keep it on internal speakers (or motu) until you are ready to sample.
now in logic, create another track. set it's input to match whatever the input is for soundflower (this is all determined by what order you added the devices in aggregate device editor). set up the same send you set up for turntable track (to bus 1, for sampling). we'll call this system track.
now when you want to sample your computer, use soundsource and set the output to soundflower (2ch). in logic, record enable /input monitor system track, MUTE the output, and turn the send up to 0. arm your mpc for sampling just as before.
the way I have described, you basically route all audio first into your computer, then use logic as the patchbay. it sounds complicated, but it's really not that bad. just think in terms of audio in / out and be logical about it to see where the signal flows.
the reason i say to MUTE the output and use a pre-fader send, is because otherwise you will hear your sampling source twice: once coming straight through logic, and twice going from logic -> send -> mpc -> back into logic. an alternative to the send is to simply change the output of each sampling track to bus 1 whenever you want to sample (i'd probably do that, personally).
to play keys from your controllerplug it in via usb to your imac. set logic up to receive it. :]
