Forget the DefTechs. If you're gonna be using the Sony for at least a while I'd generally stay away from speakers with metal dome tweeters, at least in your price range(although the Triangle Zephyrs recommended above may be an exception). This is a recipe for bright/harsh sound.
Given the size of your room you may be better off with monitors than floorstanding speakers, and you'll tend to get more for your money. One suggestion that falls right in your price range used would be Soliloquy 5.0s with their cool and beefy matching stands. The 5.0s produce a good amount of bass for their size, huge soundstage, full midrange, great detail, disappear in the room and are very efficient so should be easy for your Sony to drive effectively. You can add a sub later if you want, but either way you're off to a good start on a great system. Best of luck.
Tim
Given the size of your room you may be better off with monitors than floorstanding speakers, and you'll tend to get more for your money. One suggestion that falls right in your price range used would be Soliloquy 5.0s with their cool and beefy matching stands. The 5.0s produce a good amount of bass for their size, huge soundstage, full midrange, great detail, disappear in the room and are very efficient so should be easy for your Sony to drive effectively. You can add a sub later if you want, but either way you're off to a good start on a great system. Best of luck.
Tim