Currently I have a Marantz SR8000 (circa 2001) and Def Tech Procinema 100 surrounds, C2 center and Subwoofer. I've never really been happy with this setup. Sounds great for music (5-channel stereo is great) but movies don't blow me away. I know the Def Tech's are supposed to be pretty solid...so I'm looking for a new receiver that will make them reach their full potential. How do I decide which receiver will work best to drive these speakers?
Your Marantz is a good receiver and not your problem. If you want to be blown away watching movies, you'll want to make a serious subwoofer upgrade. For the biggest bang for the $$$, look no further than SVS. You'll be amazed by the immediate impact that a quality subwoofer will make for the movie watching experience. Once you replace the sub with a capable replacement, then evaluate whether or not you wish to upgrade further. I think you may be surprised with the results after a sub upgrade. With a new sub, you'll hear deep lows in your favorite movies that you never knew existed.