Brian, keep in mind that the actual in-wall part of the W22s(which would have to avoid the studs)is only about 3.1" wide, so this might make the installation possible even if slightly off-center.
The reason for my preferring a vertical W22(or M22)is the generally wider and smoother horizontal dispersion it has compared to a horizontal MTM configuration(I've not heard a VP150).
In that size room the QS4s should be plenty, but I note that you mention a future room, so the possibility of it being significantly bigger should be considered.
