Antman,
I had a similar Paradigm setup in a 13x23x8 room with a Yamaha rec. similar in features to your Denon. Everything sounded lifeless and dead until I ran a 5 ch. amp to the reciever main outs, all listening levels greatly improved. I suggest adding a 5ch. amp preferbly 125wpc. min.Paradigms love clean power. Set your center/rears to small,fronts to large. denon sub crossover at 60mhz, and the sub at perhaps 100mhz. The results should be well pleasing at low and moderately loud levels. Hope this helps.