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!