In a room with that many asymmetries and open areas, I’d honestly prioritize a well-placed 5.2.2 over forcing a compromised 7.1.4 layout. Good speaker positioning and sub integration will matter far more than channel count here. The KEF Q Metas are excellent for this kind of space because of their wide, controlled dispersion, so focus on getting the front stage and side surrounds symmetrical around the main seating position first.
