If you want better bass, and dont want to swap out your system, just add some dynamat around your factory speakers. I do mobile install for a living, and do dynamat in tons of cars on a weekly basis, but those all have aftermarket systems. Heres the kicker, I did my wifes focus top to bottom with dynamat to try and lower the amount of road noise, and it worked great, but the thing is, now her stock radio setup now also sounds way better. I was amazed how much better it actually sounds, with no changes to the car other than sound deadening.