I know.. stupid question

, but I am an idiot when it comes to HT.

Is my XR 55 able to biamp,

usingthe amps for the rear surrounds that I am not using. in other words i am using 5.1 instead of 7.1, can I use the other two amps for my mains?
I have the manual but I do not have a PhD in manual reading.

Thanks All
Help
mike