There are less than a handful of receivers out there that are capable of handling a full load of Polk LSI's, one of them being the Sunfire TGR401, TGR mk3 and perhaps something from the Pioneer Elite SC line.(not too sure on that one). Jay1, I like the look of that Onkyo, but I don't think that one would be up to the task when pushed. Most manufacturers like to pad their specs when it comes to what the real numbers are, and I have a bunch of experience with the LSI's... a full 4ohm load of these, all channels driven, is the most demanding load I gave to a Yamaha receiver with similar specs to that Onk, and it was too much for it to handle. I got my first Sunfire amp shortly thereafter.
The trouble here is that 4ohm loads place a lot of stress on the smaller power supply(transformer) inside most receivers, and when the demands of a movie soundtrack call instant power from these small power supplies, the receiver just cannot deliver. This causes 'clipping" that can kill speakers, or the receiver itself.
Your best play here is to get a receiver that allows for preouts. This will let you use the receiver as a preamp and allow the external amp to do the rest. Some like Emo for this , and it is not a bad choice. I would also reccomend Parasound, Sunfire and Adcom as possible alternatives.