I can add three things to this conversation. First, the weight of each product is very different. The Denon is a mere 22 or 23 pounds. The Yamaha is more. I don't know a lot, but I think the weight of the receiver means something . . . heavier being better..
Second, the app for Yamaha is pretty damn snazzy. Airplay works with the Yamaha in zone 2 as well.
Third, and most importantly, customer service for Denon is very poor in comparison to Yamaha. I was trying to make the same decision with these two models and some guy with a four letter name (Chad?) who worked for Denon actually hung up on me! Then as lack-of-luck would have it, I got him again when I called back and even a third time later on. He was terribly rude each time and it was obvious he did not like his job. Imagine if you need technical support and you have to talk to someone who hangs up on you and treats you with disdain. I chose the Yamaha for that reason. I will never consider a receiver made by Denon or their parent company again.