The SW systems are in the wall because I like the characteristics of a sealed (acoustic suspension) system. There are many drivers suitable for sealed box alignment, but few designed for infinite baffle operation. Also, it is an outside wall.
It is three separate SW systems, each having 15" and 12" drivers. Each driver has it's own amp. This is necessary because the 4 ohm driver impedance discourages parallel operation. Each 15" driver is powered by half of a CarverPro ZR1600 digital amp, 600 watts. The 12" drivers are powered by 250 watt SW "Plate amps" and their signals are equalized for phase and frequency response. I intend to use the 12" drivers to tweek the overall system performance, but in practice little or no equalization is needed. The enclosures are about 7.5 cubic feet each. The front baffle of each enclosure (which resemble coffins standing on end) is covered with acoustic foam to absorb some of the back radiation from the Magneplanars. The whole SW system is concealed behind fabric wall covering. In spite of its massive size, it is nearly invisible. (WAF you know). At present I am using 80 Hz 24 dB/octive for crossover. This makes life easy for the Maggies.
Because I designed and constructed the whole thing it didn't cost too much. I reckon it was about $3200, including 2550 watts of power amps, and sheetrock, plaster and paint to remodel the living room. Besides, the project was interesting. Better than dropping $3200 in a one hour visit to an audio shop.