Apart from not disliking the sound on my 4 door which I think is better then the 3 door. Am I missing some thing when you say your taking a feed from one of the woofers. I'd be surprised if the head unit has a crossover in it
and would rely on the speakers natural resonance so it would be a full range source, but surely you'd be tapping into either the left or right stereo feed and would not get the correct output for the sub.
Or have I got things wrong.