I think the matching center to the SM450s is hard to find, and I read on here last week people were using a different DefTech center. I would try and go with the Klipsch Reference line over the Icon series, they are a much better speaker. I believe the RB-41/51 may be in your budget, I haven't checked the prices in a while.
Samsung PN60F5300 | Denon DBP-1611 | Roku 3
Denon AVR-1713 | EMP E55Ti | EMP E56Ci | EMP E5Bi | BIC F-12
Topping TP23 | NHT SuperZero 2.0 | Velodyne DEQ-8R