Run the Behringer amp in BRIDGE mode, using the one cable from the Outlaw preamp. Connect one driver to the left channel output of the amp (from black to red NOT red to red as you would normally do with a bridge amp). Then connect the other driver to the right channel in inverted polarity i.e. with the driver's "red" terminal to the amp's black terminal and the driver's "black" terminal to the amplifier's red terminal.

All that setting a stereo amplifier to "bridge" mode does is to send the audio to one channel (usually the left) unaltered, and an inverted version of the same audio to the other channel. Usually in bridge mode the output is then taken from "red" terminal to "red" terminal. That is not what we are doing here; we are connecting it like normally, but with one channel reversed in polarity to make up for the polarity inversion done by bridging.

Trust me on this one......