Your connection scheme is correct, oaks. The Denon acting as an amp is a reasonable test of 7.1 - it's not as good an amp as the Sherbourn, but it's only driving rear surrounds.

There's no need to match the Sherbourn's 200W with a permanent rear surround amp. A lower power stereo amp would work fine, or you could get an amp like the 6x40 one you mentioned and also take care of the second zone.