I had a Sony that I was very pleased with but just for laughs and very innocently with no intention of buying....ya right...I went onto eBay and after about an hour, found a Yamaha R-V902 that had seen limited use and was in mint condition. It had been newly listed with a "Buy it Now" of only $189.00 !!. This unit sells (or, sold) new for over $500. Plus the guy was only 1/2 an hour away from me so I saved 40 bucks on shipping.
I grabbed it and I can't tell you how happy I've been with it. It is a monster. Hooked up to my Infinity Qa fronts, Bose satellites in the rear, an Advent subwoofer and a very nice homemade center channel, I've never had to turn the volume up even half way to get every window in the house rattling. Even my wife had to admit is was money well spent.
So...very quietly, very innocently, just for giggles...start shopping. You just never know...
I have the Yamaha DSP A1, my next amp will be a Mc Intosh.
I was going to say the same thing Interceptpoint said, it sounds like your dvd player is not set up to play in 5.1.