im new to the car audio world, and i have no clue about amps.

Well to be simple about it all they do is amplify the signal coming from your stereo, hence the name amplifier. It should not add anything to your music. Whatever signal goes in should be the same when it comes out just louder. You should look at THD or total harmonic distortion, the lower the number the cleaner the amp is going to sound. But dont get to hung up this number as human hearing is not that good. But if your comparing 2 amps side by side and that # has a large variance between the 2 you just might be able to hear it. Also damping factor is important, the higher the better. basically it tells you how well your amp will control your speakers. Also headroom is important, again the higher the # better. It tells you how well your amp will respond to large musical peaks, its very important in an amp that will push subwoofers. Now to power output, alot of it will depend on what subs you will be using, single 4 ohm, dual 4 ohm, 2 ohm, dual 2 ohm, single 1 ohm or dual 1 ohm. you have to match the impedence of your sub to the amplifier. You cant run a 2 ohm sub on an amp that is only rated for 4 ohms, it will overheat and go into protection. If you are planning on buying a sub that is 1 or 2 ohms make sure you buy an amp that is "high current" or the specs show that it can run a 1 ohm load. if you have any questions about what I wrote just give a holler, were all here to help.

 

Well you hook up your amp to the hu by way of the rca outputs. most aftermarket stereos will have front, rear outputs, the better ones will have front, rear and sub outputs. you run a long rca cable from the back of your headunit to the rca inputs of your amp. They do make 6 channel amps but they are quite large and quite expensive, its usually better to run one 4 channel amp and a dedicated subwoofer amp. As for your ohm question, your going in the wrong direction. If you have 2 2ohm subs most likely you will need an amp that is 1 ohm stable. BUT it depends on how you have them wired, series, parralel . It also depends on if you are running dual voice coil subs and how you have each sub wired. It would be hard to explain all the ways to wire subs. You can check out some websites, I think Fosgate and crutchfield and diagrams on how to wire subs. It would be easier to see it than to try to picture it in your mind.

 

http://www.the12volt.com/installbay/forum_posts.asp?TID=75836&PN=1

And could go to

www.bcae1.com

 

Those predone combos are usually less than good. You should start with the new HU and speakers. If you want more base then add subs(size and number depends) and an amp. After that you can dicide if you want to amp the speakers as well. What have you decided on HU and speaker wise?