4cm uses 1 input, 1 send, 1 return, 1 output
a parallel amp to powercab uses 1 output or 1 send
a second guitar or a guitar with a piezo uses 1 additional input.
stomp xl has 2 in, 2 sends, 2 returns, 2 outputs so I guess you can do it as far as hardware goes.
You need to figure out the best routing for your needs, though.