You need to get yourself an AMP, sub and upgrade the speakers, you won't be disappointed! I put in the Fark Harness from Subthumb.com, Kicker sub, JL amp and JL speakers. It sounds amazing! Check out my build thread for all the complete items and what I did to my vert. I just finished some upgrades to my engine so now all I listen too is the exhaust!
Build Thread: 2013 ZL1 Vert Delivered (Overpar73)