My infinity setup
I have a pair of Infinity RS6 Kappa 6's for my mains. I am not sure how they compare to yours as as I not familiar with your model. But I have an infinity Alpha 37c centerchannel speaker I am very happy with. I don't know current prices, but believe you can get one for aroune $150-200. And due to space constraints, I have the Wallmount Infinity ERS 210 (about $170 pr). They are really good speakers if you don't mind the hassle of installation. Currently I have a Marantz SR9300 receiver which makes them sound great, but will be ordering a new Denon AVR4308ci in the next couple of days. The Marantz sounds great, but dosn't have all the bells and whistles the new recievers do.
Maybe what you really ought to do, is send Infinity an email and ask what matches up with this speaker.