As long that you can use a 80hz x-over on all your speakers, you'll be very fine with the Marantz SR6003. Just make sure that your surrounds are not the type with a small 4 inches woofer. A 5.5" should do just fine.
And you are going to love that SR6003, compared to your Sony.
Improvement, you should notice, plus with Audyssey MultEQ, definitively.
And the 6003 is at a good deal right now too.
Bob