I spliced my signal splitter - rca converter in at the amps input. Converter fit nicely along side it and used the diagrams here for pos and neg on each channel.

Still doesn't compare to a head unit with 4 channels and L-R subwoofer jacks. Still feeding front-rear through the amp (added wires for rear channel) and the subwoofer broke out free on it's own can really kick now..