I wouldn't concern yourself too much about "sound quality" differences between the AVR's, or separate amps. Instead, I would pay close attention to the features each of the AVR has and which one has the bells and whistles you would like.

Personally, I'd go with the Denon, but that's because I've had good luck with Denon and I love their GUI and feature set. I've had issues with Marantz and will eat glass before buying another. Pioneer, I have not owned since the early 80's.