I like the idea of π cornerhorns using this push-pull configuration. For one thing, the area between the drivers is constrained, so the coupling between them is good. This will improve the distortion reduction mechanism. And for another thing, the drivers are not visible so the exposed magnet is not ugly.For your specific example, I think a pair of push-pull Alpha 10's in 3ft3 to 10ft3 tuned to 40Hz will sound very nice. If you have corners, make them π cornerhorns. If not, just use a traditional bass-reflex box. That's a couple of excellent systems that wouldn't cost much to build.