On a 2003 Yukon xl 2500 with the stock Bose system and 6 cd changer option only, there is a speaker like molding in the driver side rear cargo area panel. Is this a space for a subwoofer?? Can I add a speaker there? Is it roughed in with wiring connected to the amp/stereo? Or is there a speaker in there and mine just isn't working. I'm not really looking for "excess is best" but a little more base would be great.