John, that was my first thought, but I know nothing of Sony receivers.
DJR. Your post prompted me to go to the Denon site because I am looking at Denon for my next receiver. The 989 is a lot of receiver. Go to the Denon site and do a comparison of the 789, 889 and 989 and see if you would be giving up any features you really need by stepping down one or two models. Denon has a very nice tool for doing side by side comparisons. You might save yourself quite a bit of money doing that.
I don't know the efficiency of the M2's, but I am willing to bet that the 90 watts per channel the 789 delivers would be enough to drive them. Other than that, there are a couple of slightly downgraded components like the DACs. From what I understand, there is no longer that much difference between mid line and top tier DACs.
Blujays1: Spending Fred's money one bottle at a time, no two... Oh crap!