It's not so much as Denon is being conservative as it is they use very stable and strong power supplies which are in fact more than capable of driving 4 ohm loads. I used my older 1804 to drive my M80s and it never got any warmer than it did with the M22s. You will have no problems with the 2809.

I trust that price of $1100 was for the 1800BD and not for the package otherwise that would be an unbelieveable price.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70