This question really should go in the M-series forum: http://line6.com/support/community/support/effects/m5_m9_m13?view=discussions

As far as the controller, if it can be programmed to send out CC messages, you could probably set it up to controller the expression pedal parameters on the M13, and in turn, you could have the expression control virtually all parameters for the effects in the M13 (there are a few exceptions). You can't, however, control effects pararmeters directly via MIDI.