You obviously is an experience hobbyist so I am surprise you still seem to buy in to that so called good for music thing (no offense, sort of just kidding..) The more likely truth is, if it is good for music it is good for movies. Marantz is one of the origin of such talks, I've got to give their market the credit for being so successful over the years influencing so many believers.
Anyway, I am sure when the two are compared side by side in a controlled blind listening test, no one can tell a difference if DSPs are not involved. I do know I cannot, and will not convince anyone who believe the opposite is true lol.
Regardless, I guess you are going to keep the Denon. One thing about Denon vs Onkyo is that one seems to have a better track record on perceived reliability, but I have not seen any real proof one way or the other.