Although we don't have full details at this time if how the outputs of the "DSP box" are configured(or what it specifically does), if it takes the front left and right stereo channels and modifies(in some way)each channel for the back drivers, the modified output could be fed to the surround inputs on the receiver as Chris suggests. Then the surround outputs would be connected to the back driver terminals.

The output channels are identical in maximum output and assuming that the sections of the LFR1100 are similar in sensitivity to the M80, typical receivers with 100-150 watt ratings should be more than sufficient.

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Enjoy the music, not the equipment.