1 or 2 Rear surround speakers for 6.1 system?


I'll soon upgrade my HT system to 6.1 from 5.1. I'll have the usual L+C+R speakers in the front and 2 side surrounds and plan to add another one for the rear surround. Now, is it really necessary to have 2 speakers in the back or can I get most of the benefits with one channel/speaker?
mrcuhadare7aa
I put 2 in the rear and two on the sides. To me with recreating the theater experience being one of the primary reasons for this system, you get more robust sound with two rears. I prewired for the future 10+ system with only one rear center because the spec. implicates this. Otherwise I believe for the present 2 rears work quite well.
As far as I know there is no real 7.1 surround system. I've read it is only a manipulation of processor manufacturers,taking some info from the side surrounds and directing them to the rear.