I'm planning on adding a sub and amp to my 02 sls with the base radio. From my understanding, the audio is controlled by the RIM. Is the signal just a straight signal that heads into the RIM and then is amplified and filtered? If so, I was thinking of splicing into the signal wire prior to the RIM and converting that to RCA without a LOC. Or does anyone know at what frequency the signal is cut to the factory sub? I'm looking at either wiring a LOC to the sub wires or splicing prior to the RIM. Any thoughts?