I just picked up a 2011 Chrysler 300C with the upgraded Alpine system. Even though the system includes an 8" sub, I'm disappointed with the bass output. I don't need a ton of bass, but I'd like a little more thump out of it. I'm trying to avoid putting a sub in an enclosure in the trunk. I don't mind adding an amp for it, but I'm hoping that I can get a better sub that can just be used to replace the stock 8" sub. Any recommendations? Thanks.