No Bass Output from Rear Speakers

[gavins]

I have a 2006 C2 with the standard sound package (i.e. NOT the Bose setup). I have bought a pair of Blaupunkt THb210A self-powered subwoofers and mounted them on the rear shelf immediately behind the rear seatbacks (they actually fit perfectly, by the way). Professionally installed with power taken off a high amerage circuit (the one that powers the sunroof) and connected in parallel via the high-level inputs to each of the rear speakers. System powers up fine, but there is NO sound from the subwoofers. Professional installer thinks that it is because there is a crossover in the Porsche setup that filters out all low-frequency sound going to the rear speakers and, since the subwoofers are hooked up (in parallel) to the rear speakers, the sub woofer is only getting a mid range and high frequency signal.

If this is true I can solve the problem by hooking the subwoofers up in parallel to the door-mounted woofers instead of the rear speakers, but wanted to ask if anyone has any thoughts?