Tom, with adequate subwoofery, I think you would be ok with the center. My fear (after having used on-wall M22s) is that there is not much bass out of those enclosures. So I would strongly recommend a) a subwoofer good in the upper range (how one determines this, I haven't a clue) and b) a receiver with multiple crossovers (which I think you already have.)
I think I'm just going to make my sig consist of parentheses. (Love 'em.)