I wanna replace the speakers in my Mach 460 system

If you plan on replacing all the speakers, it's best if you replace the head unit, too. The stock system uses 1 for the tweeters, and 2 for the front and rear midwoofers, each having their own crossover point. If you are going to replace the speakers, it's easiest to just bypass the amps altogether and run the speakers straight off the head. If you're not running any external amps, running coaxils in the doors will sound fine, you don't really need to run a component set unless you want to be able to adjust for imaging, or you want something with a little more powerhandling.