Please keep in mind, no matter what brand/model in-wall sub you choose, you need to physically de-couple the device from the wall board and studs, otherwise substantial coloration will occur. A few small stiff rubber washers or short hang brace will not be sufficient(unless it is a very specialized hanging brace; I would need to see photos of the kit to let you know if it will be effective). It is possible to retro-fit such a mounting system into any application with a little know-how. I can make recommendations if needed.
-Chris