Unfortunately, while a manifold type IB sub may not transmit mechanical vibrations to the structure, the sound backwave from the drivers are not isolated from the rest of the house. The self-contained systems from Velodyne, Def Tech, Triad, etc. are what the OP is looking for. The better systems perform comparably to their in-room counterparts but may be cost prohibitive. In a room your size, I would think two sub systems would provide the best performance. But of course that's a matter of preference.
