Sorry to hear that your speakers suck.
When I was playing around with my own designs for matrix multichannel, I discovered that a rear speaker operating out of phase with the fronts could very greatly boost low frequency response. Think of it this way...you are exciting the room air in a push/pull manner rather than single ended. The boost frequency depends on the distance from front to back speakers, and on relative phasing, although I didn't experiment with phase.
Frankly I doubt that an inactive speaker will soak up much sound. The cone area is very small compared with that used for room sound absorption devices, and the cone material is not particularly absorbant.
When I was playing around with my own designs for matrix multichannel, I discovered that a rear speaker operating out of phase with the fronts could very greatly boost low frequency response. Think of it this way...you are exciting the room air in a push/pull manner rather than single ended. The boost frequency depends on the distance from front to back speakers, and on relative phasing, although I didn't experiment with phase.
Frankly I doubt that an inactive speaker will soak up much sound. The cone area is very small compared with that used for room sound absorption devices, and the cone material is not particularly absorbant.