just a note... the only "real" difference between the Polk Monitor line and the TSi line is upgraded esthetics. For all practical purposes the "guts" are the same, or very nearly so, and it comes down to a huge price differential for improved "looks".
To compare apples to apples, you would need to consider the TSi500 as a direct competitor for the Monitor 70's. The TSi400 = Monitor 60.
pricing and free shipping, the Monitor series wins hands down. (if you can wait and watch for one of their coupon sales on the Monitor 70's, you can save even more $$$).
As to a receiver, start with these models in each manufacturer's lineup and then move up-price until you find the receiver with all the "features" you want. Denon 590, Onkyo SR507, Yamaha V465, Pioneer 819. I have not keep up with the Harman/Kardon lineup, but I'm sure others will help out here. Each of these models has full audio and video processing, including decoding lossless HD audio codecs, over HDMI cables.
If you want to consider another speaker line-up, price out a full system of Infinity Primus speakers, starting with the P362 towers. Unless you find a great sale, they are a little more expensive than the Polk's, but they are the direct competition to the Polk Monitors as a super "bang for the buck" speaker setup.