I certainly have less knowledge about this than Gonk, but I can give you some practical experience.

I use towers as mains and they are set to Large. My center and surrounds are set to Small. Speakers set to Large on the 1070 have no X-over. You cannot change the setting from None to anything else.

When I play stereo FM, TV, conventional CD, my sub does not wake up from sleep mode because the 1070 is not sending it any signal. Only when a 5.1 source comes on line does the sub wake up. I assume the bass from my mains does not become part of the LFE, and does not come back to the mains.