well.. .your first mistake is putting a center chan in. if you want clean sound you want to reduce and control the point sources of sound. you'll get some weird cancelations and lobing if you add that center chan speaker.
my suggestion is to go with components (you can get low end focals for $200), drop the center chan and the amp for it and put it towards your front speakers. also, leave out the dash speakers. if you have the ability to crossover with your soundcard then you could also take that amp and use it to run an active setup. you could get some dayton rs180's and maybe a seas neo tweeter (or dayton tweeter... or north creek if you have the space...or various others) that'll cost you under 150 bucks and you'll have a great set of component speakers that you can tune for your individual car/truck.