Welcome. I have the same set up 80/500 with a Denon 3808. works great. Once you learn the GUI on the Denon, you'll be good to go. As for mounting heights, all the experts will say the same height as you ears ( when sitting down ), but I have my QS8's mounted at 6.5 ft and they sound fine. Personally, I think you could get away with anywhere from 3-7 ft and be fine. As for the Center Channel, you could go above or below your screen. I have mine mounted below using the Axiom CC 18" mount. Kinda expensive for what it is, but the mounting holes match up perfect and it's very sturdy if you have kids.
Enjoy!
JD
