Are you using 1080p resolution for your devices going through the Denon?
I'm curious if my problems are related to the high resolution. When I connect my XBOX and my DVD player directly to the TV at 1080p, I have no flickering problems at all from either device. But going through the Denon they both flicker, the XBOX especially. However, my Comcast Motorola DVR which is only outputting 1080i doesn't flicker at all.
I've tried everything I can think of, even switched cables around trying different cables to make sure the problem was not related to bad HDMI cables (I use the top of the line BlueJeans HDMI cables, short runs of 3 and 4 feet). I also downloaded all the patches from Denon, Microsoft and Oppo, which helped a little, but it still flickers quite a bit.
I talked to Denon twice, they insist it's not their problem, and one guy started telling me Oppo is cheap Korean crap. I inquired if they would consider repairing my receiver, but the problem is they want me to send it in at my own expense, and they want 6-8 weeks before they return it. That's just unbearable for me.
I'm so frustrated with this damn annoying flickering, I have seriously considered buying another receiver. However, I heard the Pioneer Elite receivers also have this problem. I don't know about others.