So, I just bought an e46 M3 Convertible (2002). It has a Rockford Fosgate P200 Punch amplifier, a stock business CD head unit, a sound gate LOC, and a BSW sub in the ski pass. The stereo works fine, but I get no sound from the sub at all. I need some genius help here guys! Here's what I've checked/done so far:

I checked all the electrical connections and voltages. The amp turns on, runs at full battery voltage, and the protection light is not on. Whoever did the install did it nice and clean. Wire ties every 6", power correctly fused, etc. The LOC is tied into the rear speaker wires before the factory HK sub. I understand this to be a balanced differential signal.

I read up on the amp, and it accepts the balanced differential inputs, so I wired it up according to the manufactures directions to test it, in case the LOC was no good. No sounds still. Oddly enough, the manufacture requires the + signal from the head unit to go to the center RCA pin, and the shield of the RCA to go to vehicle ground. Doing this gives me a reference voltage of 5.5v across the RCA terminals. The rear speakers that are tapped into work just fine. All the connections tone out properly as well.

I bought another amp to test it. I couldn't get sound out of it either… Even the wires to the sub itself from the amp tone out just fine. I tested it with the LOC installed. The testing amp does not accept balanced inputs, so no testing there..

I've installed stereos before, and competition stuff a long time ago. I can't see any reason why I'm not getting any sound. I'm new to BMWs and to Harmon Kardon though. Is there something stupid that I'm missing?

Thanks for all the help and Happy New Year!