B&W CWM 7.3 and or 7.4

Novice seeking advice on amp to drive either the CWM 7.3 and or 7.4 in wall speaker. http://www.bowers-wilkins.com/Speakers/Custom_Installation/CI_Series/CI-700.html

I tried search function and did not find much on this topic (or perhaps I searched incorrectly).

I will be running this in-wall system in a den. Like a warmer sound. Budget is around $3500 for the amp. Names I am considering are the Luxman 505-UX, Krell S-300, Rotel Separates.

Other question would be related to performance of in-wall speakers. Should I even spend $$ on a nicer amp or are in wall speakers limited in terms of performance, laws of diminishing returns?

Not allowed to have towers, as the speakers are to be "invisible".