If the 806 has the features you want, I wouldn't hesitate to get one. If you don't like it you could still resell it for the same amount as $500 is a steal.
The 806 is a very stout performer from the lab testing/reviews, it lacks some of the other features you would be paying for with the 3808, biggest ones being the GUI and network connectivity, for which you pay a premium. Onkyos are also known for running a little warmer than Denons so there must be a few cents saved in heat sink materials etc. Denon has a pretty rock solid image and name, another thing you end up paying for.
806 review 
