I don't know if it is possible or not. Looking at it from the perspective of a mechanical engineer, I would think the central challenge there would be providing a path for the analog signal to "flow" to the ADC and into the DSP for bass managment to allow for the creation of a subwoofer signal. Once that was done, it would presumably be possible to pipe that sub signal through a DAC and out without interfering with the original analog signal to the mains. Whether that change to the signal path is software or not is far beyond me. If it were water or air, I could probably make a better guess about the logistics.