Hi Kanifi,
First make sure that the MIDI/OUTPUT setting on the Factor pedals is set to 'THRU.' That way you can cascade MIDI from one pedal to another via the OUT/THRU MIDI jack.
To set which presets will be called up, go to the MIDI/RCV MAP menu and you will find MIDI Program change numbers in the left column and corresponding Factor Presets in the right column. You can change which Factor Presets will load for each MIDI Program change sent by your musicom lab unit.
-Alan
