Here are the differences I see:
Both the Marantz 5009 and 6009 have 7.1 RCA inputs (likely not an issue), Denon and Yamaha do not.
Yamaha does not have Audyssey DynamicEQ (but may have a capable Yamaha equivalent), also not sure how YPAO compares to Audyssey.
Denon and Marantz have pre-outs, Yamaha does not.
6009 has phono inputs
Curious why you decided on the 6009 over the 5009, the main difference I see is multi-room video.
As a rule, I agree with you. Denon offers more features and equal (or slightly better)power for the same money. I just like the port style of the Marantz
!