I have not heard the Yamaha, but have had two 4520. The first one faulty and the second one maybe the worst sounding avr I ever owned. I did have a Yamaha A1000 and it was pretty good, much more enjoyable than the Denon. It would not even be close for me to decide.
Also be sure to check which is more reliable, call any installer, ask which gives them less headache..... I don't even own a Yamaha or care for their sound very much but the newer Denons are not like the old, which was reliable but just ok for sound to start.
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