I would use the amps in the receiver and never look back.
Yeah, that’s pretty much what I said. I think the amps in the Marantz Cinema-40 are great enough for the R11.
I mentioned that I know a person who got the R11 and Yamaha RX-A4A. He still says he wants an ATI amp. But he’s been using the A4A with the R11 for a year now and loving it everyday.
Apparently the A4A is doing just fine without any external amps. Getting an external amp would be just a luxury, not a necessity.
And the Cinema 40 will do just fine with the KEF without any external amps.