Multichannel plus two channel mixing it up help needed

I've got an Arcam AVR600 and a plinius M8 and two P10's to make use of.

how can I best set things up, for example, is it possible to pre out the left and right channel to my P10 that powers my stereo system but have the arcam power all the other channels? I don't want to fork out for two speaker cable runs or have to swap speaker cable.

help appreciated.