Unlike the most of you I am generally happy with the stock radio, but I am looking for little more bass...I don't have the bose and am looking for effective and not costly way to add a little more bass. I notice that they door speakers seam to be doing a good job, but the rear speakers behind the head rest don't seem to be adding too much of anything? I was thinking maybe an aftermarket sub placed where the stock bose would go, but not sure of cost and if that means I would need a new head unit and how all of this may affect my warranty. Any suggestions??