What do I need to purchase for a car sound system?

really it doesn't matter what size amp you get and it depends on how many subs that you want, and yes there is a big difference in music when you upgrade, and no your factory speakers will not blow they will blow if you put a amp on them but just a regular radio they will be ok.

The joy of a personal car stereo system is that it is what you make of it. I'm just going to go down your list one-by-one and help you out. For the amplifier set up it just depends how many speakers you want to power with it and how much power you want going to each speaker. A 4-channel amp has the capability to power up to 4 speakers (FL, FR, RL, RR typically), where as the 2-channel will only cover one left and one right. As far as amp power, that is limited by the amount of power your alternator can supply, the amount of power your speakers and wiring can handle, and how powerful of an amp you can afford. You just have to keep in mind how many speakers you are powering and what is affordable for you. As far as audio quality, the quality of the sound is only as good as the weakest link in the system. You can achieve decent sound from any amp setup if all your components are of quality. Price is going to be determined by brand, size, and quality. Know how much you can spend on amplifiers, how many amplifiers you would want (i.e. do you want one 4-channel amplifier or two 2-channel amplifiers) and how much power you want total. In my eyes a decent amp has at least 50-watts per speaker ( that could be either a 200W 4-channel, or a 100W 2-channel), and anything above there is icing on the cake, depending on how loud you want your system. Just remember, quantity counts, but quality counts for more. A good equalizer wouldn't hurt either. As far as subwoofers are concerned this is again up to preference. It isn't the number of subs that matter, but the total size and power of your sub system that matters. It's surface area and area of travel that matter with subwoofers. The more surface area on the speaker cone, and the farther the cone can travel, the louder the subs can be. A well built subwoofer and enclosure, mono-channel amp, and a frequency filter can go along way. The frequency filter helps because the human ear cannot pick up sounds lower than 20Hz, so if you are trying to push frequencies lower than that through your system, all you are going to hear will be vibrations and white noise from everything else around you reverberating. As far as the stock speakers are concerned, if you are adding additional amplification to the stereo system, you will want to replace both the stock speakers and wires. The stock system is not designed to handle any more than what the stock stereo was designed to output, so if you try to push more power through that system you will just do damage and ultimately have to replace them anyway. If you are already pulling the audio system apart to replace some components, it would be cheaper and easier to just replace everything at the same time instead of having to go back and replace the cones and wiring you fry, thus pulling apart everything again anyway. A couple things you didn't mention in your set up that you might also want to consider if you want a really good sounding system would be the equalizer like I mentioned earlier, some capacitors to help provide extra power to the amps without them cutting out under load, large gauge wiring to handle the extra power flow, and some insulation to help prevent nasty vibrations from the interior trim and body panels vibrating with the power.