Two Questions. Is there a way to add an amp and upgrade the 8 inch sub I have a GLS with the Navigation. I was thinking of adding a JL sub to the system and an Amp hidden somewhere in the Trunk. Second thing is that I noticed that while driving the sound does go up and down with the auto volume, but it is still not that loud. is there a limiter that wont let it go past a certain point so that it does not blow the speakers casue even all the way up there is no distortion really. thanks guys.