It will sound better with just an amp and speaker upgrade, but to get a much higer quality sound I would reccomend upgrading to a headunit that uses RCA preouts. Going to get a higher quality sound with more clarity then a factory head unit.
Focal is a great brand of speaker, but a little pricier than some brands, but to me the price increase is worth it. Most amps are great, I would reccomend, Kicker, JL, or Diamond Audio, most major brands are great, I would stay away from Sony or Rockford Fosgate. Go to a car audio Specialty store, don't go to a place like Best Buy or Circuit City.
When you say base, I assume you mean you want a subwoofer which produces "bass." I would reccomend JL audio, Kicker, Eclipse, Diamond Audio, Inifinity, once again all major brands are good, just stay away from Sony or RF, and I would still stay away from places like Best Buy...
With car stereo equipment you always get what you pay for, if you buy an amp from one company that is 50x4 and it is 50 bucks, and an amp from another that is also 50x4 but is 200, that one costs more for a reason, it will be more reliable, higher quality sound and parts, etc. Car audio is a hard thing to look at ratings for, there is usually no industry standard for measuring things. It's like when you buy a factory head unit and it says it has a 50x4 amp built into it...that is just impossible. They way they measure it they were able to get a power reading of 50x4 for maybe half a second and at some wierd frequency.
Hope that helps.
