So my 92 has a non-JBL premium sound car with its super gay tape player has got to go. The radio isn't bad, but the receiver I picked up has a USB input and headphone input which will help when I drive through Nebraska and Eastern Colorado. The problem I'm having is that the radio has all 3 plugs at the back: it has the regular grey and black non-premium sound connectors as well as the small, square black premium sound plug. I'd prefer not to buy the high-low converter to run the aftermarket deck through the factory amp, but I'm not sure if the unused non-premium sound black rectangular plug (bolted to a blank in the back of the factory radio) is wired all the way to the speakers or not. None of the stereo shops around here can answer this question and apparently, neither can CVN with its larger amount of users which shocks the shit out of me. Any of you guys screwed with this before?