There's nothing wrong with a "low-end" Sony or Pioneer amp. My dad had his Sony 2 Channel reciever for ten years before it burned out on him(in the reciever's defense, my dad was playing 4 Bose speakers simultaneously on the A+B configuration the entire 10 years). My Sony 5 channel amp I've had for two years and it has shown no signs of letting up (although I plan to upgrade it WAY before it would need replacing). Will the Denon's and HK's provide a little more power and features? Yes, but a simple Sony or Pioneer will play 5.1 in both DD or DTS modes. And thats all you really need. Now I along with everyone else would recommend investing a little more in the reciever, but don't let everyone else "muscle" you into buying something you don't want to.
My Dad's PSB's sound just as good playing through my Sony STR DE 595 as they do through his Denon 1604.
