It's a little tough, because it's a combination of programming the MC6 and setting up the midi mapping in the C4. But I'll try to explain the process. Also keep in mind that the C4 was only doing filter duty. I used an Iron Ether Subterranea as the synth tone going in. You could totally do it all within the C4 though.
C4 Patch setup:
I set up a 4 pole low-pass filter patch in the C4 to be controlled by LFO 2. I also set up expression as control source 1 for the lfo speed to let me use an expression pedal.
C4 mapping:
I went into the midi mapping and assigned midi values to lfo 2 multiply (cc94), Remote Tap Tempo (cc93), and to external control source 1 (cc92)
MC6 Programming
I set up my MC6 so that the expression pedal sends Midi cc100. This is the default expression input on the C4.
I have a bank set up on the MC6 to control subdivisions and tap control.
I set up buttons for x1 (cc94 = 0) x2 (cc94 = 1) x3 (cc94 = 2) and x4 (cc94 = 3)
I set up a midi command for tap tempo. I set it up so when using this it also sends midi to disable the expression control. It sends (cc93 = 0) and (cc92 = 0)
If I want to use the expression pedal again I have another command on the MC to enable it by sending (cc92 = 3)
Hope this makes sense!