Home Theater System Advice

I personally would sell the Infinity's(or maybe move to another room), and start over with a COMPLETE new system! You need to concentrate on getting a cohesive matching speaker package together first, then find out what receiver/amp/processor, etc, you need.
Are you doing equal music to Movies? Any priorities there?
What's your room set up like?

I would get the Outlaw 1050 receiver. This is a great sounding unit with reasonable power. Good used samples can be found for about $400. I'd recommend that you use the Infinitesimal IVs as the surround speakers and get some larger Infinity speakers for the front L/R/C. The Kappa center, for example, sells for about $550 on the used market. There are several Kappa L/R models that sell for under $1000 for the pair used.