There is a great how-to here:
viewtopic.php?f=11&t=97274It's technically supposed to be for the MPC4000 and logic 8 but it should be pretty much the same for you.
The answer to your actual question is, a midi cable from MPC midi OUT to your audio interface midi IN.
Then configure logic channels to respond to particular midi channels.
It's in the track properties window on the left hand side when you select a channel in arrange view. Configure each instrument to a different channel.
You might need to do this:
choose Settings > Recording, and under MIDI, select Auto demix by channel if multitrack recording.
if you are recording multiple channels at once.
Don't worry about sync yet. Just make sure Logic is receiving the midi information, then you can move on to sync.