I'm not looking into building a entire system. Just replacing the stock speakers with some better ones. Get some better sound maybe turn the volume up a little louder and get some more bass. Should I replace the rears and the doors. How much of an improvement do you think I would see if I just went to best buy and got like some nice aftermarkert what 6x9's and 4" , 5" door speakers. I have the 6mt with premiem sound.