http://usa.denon.com/ProductDetails/554.asp
http://www.yamaha.com/yec/products/productdetail.html?CNTID=200506&CTID=5000300
I have the 659 and was torn between it and the 2106 when shopping for the receiver. I found the Denon to be a bit more powerful than the Yamaha at the same db levels, great salesman...we played around back and forth with both for over an hour with a wide variety of my fav cd's, but not enough to warrant blowing my budget and pissing off my wife for the extra $200.
The primary features are generally similar, see specs on above links, with each having some the other brand does not. I did like the Burr-Brown Bit DAC's for all channels because of their recognition for quality.
It has been 4 months since buying the 659 and I am quite satisfied with its' power, features and performance. No upgraditis hehehe. It has all the power I can use and then some. The set up system is good but not great, setting my front speakers to large and setting my sub at too low a level but the spl meter remedied that error. Otherwise I am satisfied with the rest of the set up settings...eq, speaker distance...
I play around with the varied sound fields here and there and find them to be enjoyable and different enough to warrant going through all the effort to push buttons on the remote...oh the effort, oh the toil hehehe...There are enough to get some very different sounds but not so many that it is ridiculous.
I suppose in the end it depends on how they sound to your ears with your listening material and budget.
Many here espouse refurbs and used equiptment however I do not. For my money I want it out of the box new and unhandled with, hopefully, no history of problems in its' past.
Good luck and keep us informed.