I think the only way to go is with the Subthumb.com system. I installed a Kicker 10" sub and JL 700/5 AMP. I also installed Dynamat all over everywhere I could reach to include the complete trunk and interior. I replaced the stock speakers with JL's 6.5's, tweeters, crossovers and 3.5's in the rear seat. I installed batting behind the rear speaker area in all of the empty cavity behind the sub speaker. You'll see after you get the seat out and speaker removed what I'm talking about. This stereo system sounds amazing now!! Check out the build thread for a detailed step by step on everything Iv'e done so far.
Build Thread: 2013 ZL1 Vert Delivered (Overpar73)