I'm suggesting what you need for the optimum experience. You have a lot of cubes as you say, so to pressurize it, you need a lot of subbage...particularly for movies. Sitting back 15 or 20 feet also means you need a system with significant sound pressure capability. Sure you can use the Paradigms and QS8s with a 500 sub for that room but don't expect wonder from it.

House of the Rising Sone
Out in the mid or far field
Dedicated mid-woofers are over-rated