what's the primary use of your theater: movies or music? Is there anything you specifically dislike in your Infinity speakers, or any characteristic you wouldn't want your new speakers to have? Conversely, is there something you especially like your current speakers, which you'd want the new ones to also exhibit? Is design gonna be a factor at all?
As for the sub, bass is adirectional and doesn't need to be timber-matched, so any subwoofer will work well with anything you purchase. For movies, it's vital to get deep bass even at the cost of speed; for music it's advisable to favor speed over extension. Having both is obviously a best case scenario. Check out the offerings from companies like Epik, HSU, SVS, JL Audio, Velodyne, Sunfire, et cetera. They all make good products for pretty much every price range.
Last but not least, as I always suggest, check out the second-hand market: it will often get you a lot more value for your money compared to buying new stuff ;-)