Umm, yeah - what he said. (No comment as to why it took the rest of us this long to skip to the underlying solution...) That definitely seems like the cleanest approach in a lot of ways. Unbalanced from the 990 to the A5 for center and surrounds, then unbalanced left/right from both 990 and ZD to a switch box ahead of the A5 (or just manually switch cables around, although I'd personally prefer to track down a good quality switch box).