Don, yes you're right that the suggested viewing and listening distances are quite a bit different. For your 120" screen example a 12' distance could be used as a compromise that should work acceptably for both visual and audible factors.
As Dean questioned, however, why is the AT screen concept so attractive? Mains positioned outside a regular screen and an identical or at least similar(e.g., M22 with M80s)vertical center below it would work well. Or, if the AT screen is used, consider placing only the center actually behind it, with the mains wider and outside.
