The Sony will sound better with a seperate amp.
With your room and speakers, I'd buy the biggest amp that I could afford.I don't think you'll ever regret it.
+1. I found a noticeable difference when upgrading from a good Yamaha receiver to the receiver and 7125. Moving up to the 7500 improved the sound quality even more. I recommend going with the larger, separate amp. The Outlaw 30 day guarantee allows you to decide if that combination fulfills your audio needs.
Rob