I'm still kind of new at the home theatre thing, but actually have some pretty good knoweledge of how to make a vehicle sound good. Just like home audio (most those kids dont do this), its critical that you step up and spend money on all the accessories like fuses, noise dampening materials, proper boxes, good crossovers blah blah blah blah... Most aftermarket head units are capable of powering most two way coaxials on the market and this method works just fine. if you invest in a component speaker set, an amp may be necessary. The info here so far on subs is correct. NOBODY HAS TWO 15's that sound incredible. My best setup included every component from Eclipse audio. I had a pre-amp head unit with an 8volt preout, an eclipse premium 4 channel amp (only 50x4), Their point source series components up front and in back and a titanium 10" sub with an eclipse premium 700 watt amp. I used good cables, good connections, applied l-pads to the tweeters (trick i learned in an audioholics DIY forum) and there was some music i would have rathered listned to in my car(sitting still of course)than inside my home. I found that the key to good car audio is spending a little more money on good components. upgrade a piece at a time so you can tell what makes a difference...