Because he is, I think, using the 7011 as a processor and while it has 9 amps built in you cannot unfortunately treat that as a generic pool. If he is using the Monolith for 7 main channels then to do 4 heights/overheads then he likely needs at least a stereo amp in addition to do the other pair. It is a pain that whilst it can, to a degree, assign some amps, the flexibly may not allow the precise use he is looking for.
5.1.4 or 7.1.2 would not be problem at all with what he now has.
A nice little stereo amp on top of the Marantz would likely not be too much of a problem regarding heat for either if it does not complicate the wiring too much.