For better or worse (mebbe worse) I often look at it from an amp perspective. That being said, the 606 does not have preouts. The 805 will probably have the beefiest amp. But the question is if you even really would benefit from one.
Otherwise, people enjoy Denon for their fine reputation and general reliability, if cryptic manuals due to poor translations from Japanese. Yamaha has plenty of fans here and elsewhere, although speaker/sub x-over mgmt is typically more limited. However, I doubt you need multiple x-over points/selections with your set.
FWIW, I use a refurbed 805 as a pre. There weren't many choices at the time of my purchase, and it was cheap as anything else that had hi def audio support, preouts, and matrixing capabilities at the time.
Flip a coin.