Usually you want to timbre match the front setup, but ultimately, it's whatever sounds good to you.
Try all Quintets up front and the RB35's in the rear.
Do you have an Audyssey setup on your receiver?
If it were me, I'd be half tempted to get a Klipsch center channel that would play nice with the RB35's and put the Quintets in the back for surround. Maybe sell the Quintet center to offset some of the cost for the new center.