no you can basically have 16 on each out so 32 devices daisy chained by one MPC. This all has with the gear you have and if there are thrus. Most professioanl midi gear has a thru port. MIDI holds sixteen channels. Thats why in track mode you see 1a, 2a,3a, excetra. Midi is pretty simple its just confusing to understand the basics. The M usic P roduction C enter. =MPC. is a MIDI sequencer. The only sounds that are coming from it are what the MPCs sequencer is telling the MPCs internal sampler. Hence loading samples. MIDI is basically remote control for all your stuff.
ex.
A midi controller keyboard or the MPC's pads would be control devices. The keys and pads are sending MIDI signals saying to the devices that HAVE the sounds in them to turn on and turn off at what velocity legnth the control device (pads, keys,) are played. People think that MIDI has anything to do with Audio. It is like if say I wanted to change channel 23 to 64 on the televison. I would type that into the remote control instead of getting up and pressing the actual buttons. MIDI is like that. So you can control then slave other device to the MPC. It will acts as the remote telling its sampler and your synth when to play that kick and sanre and those synth lines. The sequnecr means it records the MIDI data and plays back that data realtime. Thats what your doin when you are hit REC + Play You are sequencing.
Check this site out for a good grasp of MIDI.
http://www.borg.com/~jglatt/tutr/miditutr.htm
all mpc users are using midi daily and dont even know. learn this ish
peace