So I brought my car down to a local shop to find out some information on whether or not I could keep the factory dash/cd changer in my 04 grand prix and add speakers and amps to the car, but he said with the monsoon system I couldn't because the factory head unit only had preamp outputs and he could only run a subwoofer off of it...However my amplifers have preamp inputs so shouldn't that work or is it not possible to upgrade speakers with out a new HU.