Yes, you have to use the other two channels. But you could always put in a cheapo 2 channel receiver in and hook up to the multizone stuff when you go 6.1. ABus is cool because it doesn't just provide IR control of the reciever, it also provides amplification and volume control for a set of speakers. They all seem to be in wall units (like light switches) such as the H/K AB1.

I am the Doctor, and THIS... is my SPOON!