A wall with four Digital Designs Z series subs and four DC 10k amps, a whole bunch of super tweeters and ten inch midranges in the doors. And 500 square feet of deadener, ten XS Power batteries, and a bank of four Mechman alternators. That should get you started.
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In all seriousness though, just read the forums a bit. You honestly gave us no information and asked the most nonspecific of questions. What are you trying to accomplish? What is your budget? You know, some ACTUAL DETAILS about what you're wanting to do. Rather than just asking the most oblivious of questions.