Hey there,
not sure if you got this question answered yet, but here goes my point of view.
1/ The Denon is a Transport, so depending on your AVR the Yamaha might have a better DAC and thus a better audio quality. If you have a great AVR, then for Audio the Denon would be the better choice, as being a transport, it sends any and all signals from your CD, DVD, DVD-Audio, SACD and Blu-Ray directly without manipulation, at all, as pure as it gets. (The Yamaha is capable of doing that too, but sometimes, even the presence of extra chips on the circuit board can cause sound deterioration and interference, so IMO, less is more here.)
2/ Denon and Marantz are the same company, they are together with McIntosh in the same group, but as you can tell, all 3 brands have a slightly different target audience. Denon and Marantz are mid to high class, with Denon appealing to the modern guy, whereas Marantz appealing to the classy one. Denon uses plastics more often, where Marantz goes all metal. McIntosh is in a different world altogether though.
Hope this helps.
BTW, you can watch my unboxing video of the denon here: http://youtu.be/8DLSEMQNkOE