I have an '02 Sonata GLS with the OEM H290 head unit (AM/FM/CD/Cassette). I've replaced the rear speakers and am now considering adding a subwoofer. Does anyone know the specs of the head unit? There is a seperate amplifier in the rear trunk, but I don't know if it is recieving a preamp or a high-level signal from the head unit. The Hyundai technical website isn't very helpful. Thanks!