I have never been overly impressed with HDMI connections - they just never feel secure.
When you consider the competition was DVI with it's super secure screw fixings, which you never had to check after pushing an item of equiment back in place. Why they could not just add sound to DVI or make HDMI with screws is beyond me - there's progress for you !
I got fed up of cable headaches and have sunk my whole unit through the stud wall (looks so in keeping with my plasma being on the wall) and have very large cupboards in the adjoing room where I can simply plug in cables with no hassle - impresses equally sad minded people also
As for your Denon then it may be worthwhile taking your lead to your Denon supplier and plug it into same amp and check that way.
Cheers.