My X4400H was quite finicky in the beginning too, had to do the unplugging (TV and or AVR), changing sequence routinely, but after a few FW updates (no idea which one did the trick) it finally settling down and has been working 99% of the time. Once in the blue moon when it wouldn't work (no sound), I would switch the AVR off with the remote and turn it back on then all would be good again.
So based on the symptoms, I think the 1% problem has to do with imperfect HDMI handshaking that appeared to be largely fixable via FW. As to whether the TV (Sony in this case), or the AVR, or both was/were the problem I would never know as both have a few FW updates. I would think since the OP has the two model years newer Denon than mine, probably the TV is responsible but again, hard to know.