Floor standing subwoofers are, in general, far superior to in-walls.
I'm not sure if rear height surrounds are an ideal situation. Take a look at the new 2015 Denon model manuals (pdf) for speaker layout diagrams. The rear surrounds/surround d backs should be ear level. Height speakers should be in-ceiling above the main listening position or forward, IIRC. Definitely look at those manuals.