I've had bad luck with all the refurbished AVR/ pre-pro I've bought.
I feel your pain.
I know you bought several from "clearance" companies that sell everything from toaster ovens to air cleaners to audio gear and had bad luck and bad Customer Service.
Did you ever try buying one from Accessories4Less?
I have bought over a dozen items from them and not had one problem. However, when I did screw up and thought an AVR was malfunctioning, I was very happy with how easily I got a replacement unit. When the replacement did the same thing as the first, I realized that I was mistaken, I just did not have the settings where they should have been.
So you are 0 for 5?
I am 12 for 12!
That should tell you something!
Companies like Damark and One Call seem to take their defective returns and recycle them by sending them out to the next guy to order that item.
If you are 0 for 5 and these are supposed to be
factory refurbished (which is a very important distinction) units, something is wrong when I am 12 for 12 (better than half of these are Denon's like you had problems with).