In my part of the world getting a Denon 3805 is about $400 more than the 990 was. So I went with the 990. But otherwise my choice would have been the Denon as a preamp with an Outlaw amp(s)..
Obviously Monos have there advantages. The only disadvantage I can see is having 7 of them may take more circuits than some people have wired. If you can afford the monos, go that way..
Besides, if one breaks, you can still listen to 5.1 or 6.1, with a combo amp you have nothing..