This is my son's car and he had the amp and the subs from a previous car we traded in. Is it overkill? In my opinion yes, but when I was his age, it was just right. I was pleasantly surprised at the amount of additional control the line out converter offered me, so I am able to adjust the settings appropriately. Overall, adding the bass seems to at least provided the audio illusion of making the factory speakers sound better mainly because I didn't have to turn up the bass settings on the stereo. My son thinks the overall sound is very good. Of course adding new speakers would probably enhance the mid/highs but he's happy with it. The only other thing we are going to add is the CN-M5 retro-fit from compass-nav. It should be here within the next few days and I'm hoping that the 10 band EQ it offers will allow further sound refinements. As for rattles, everything seems very tight (no rattles) at the moment, but of course over time, rattles are inevitable.