Noble, if they are built into walls they are no longer dipoles and trying to get the resonances out of walls is a nightmare. The limiting factor in all Maggies with a ribbon tweeter is the tweeter. It is a wonderful tweeter, some say the best ever made but it is delicate. Adding more panels is not going to increase the system overall output. I can't speak about sound quality because I have never heard it done. Quality first, output second.
The key with any linear array system is to keep it functioning as a linear array over the entire audio and subsonic spectrum so that power output remains even from top to bottom. There is always a weak link in the chain. In my case even with 800 class A watts at my disposal it is the satellite amplifiers. At that point I am putting out 110 db which from most peoples stand point is absurd. Comfortably loud is 95 db. At 110 db my subs are hardly working. You have to make your subs a linear array which you can do either vertically with two sub towers from floor all the way to the ceiling or horizontally with drivers all along the front wall from corner to corner. It is easier to control resonance in a smaller enclosure so I favor multiple small cabinets over one or two large ones. Your explanation of Q was excellent. I build my subs with a higher Q than usual 0.76. I depend on amplifiers with very high damping factors to control the drivers. This increases efficiency. How many you need depends on the length of your wall and the crossover frequency you want to use. To take the most advantage of boundary gain two have to be in corners and the others along the floor wall boundary. I use a cross over of 125 Hz so the individual drivers have to be 6 feet or closer together. The wall is 16 feet so a total of four subs will do the trick. Because of boundary efficiency with room control I am flat down to 16 Hz where I roll the party off steeply to prevent issues with the turntable. If you want to use a higher crossover you have to space the drivers closer together. If you have a longer wall you will need more drivers. A point source system is different. If you used this type of sub array with a point source system as you backed away from the speakers the subs would become overpowering. As Atmasphere suggested a two sub system tuned to the listening position would work fine or if you wanted more even response throughout the room a "Swarm" would be fine. I use 12 inch drivers exclusively by the way. I am working on a new set of balanced force subs with octagonal enclosures made of 2" MDF. They are essentially a tube with a 12" driver in each end opposing each other, canceling out all Newtonian forces. Same Q.
