The Infinities aren't aimable, so make sure you know exactly where to place them.
I have a pair of ERS 310's still in the boxes in my attic that I bought to be surrounds for my P362's. The tweeters aren't aimable. (Leave me alone about the installs. I bought wire and plates to do it this spring, but a certain female has kept me busy w/ wedding stuff. I ain't climbing into a 130 degree attic right now anyway.)
Why didn't you insist the installer get more Pinnacle's to match your fronts?