iv been through the ringer several times when it comes to sound systems im no installer but i can tell you from experience spend the money THE FIRST TIME and youll end up saving yourself money and time. when ever you put in after market speakers you should ALWAYS add an amp to them because those speakers require more watts to power them if you under power them they sound bad and if you think they sound good now they will sound amazing when you add a proper amp to them, truste me im speaking from experience, and the amp that comes with the shaker systems no offense but they are a joke so replace that to. and as far as keeping the sync all you have to do is by an adapter that plugs into your factory head unit and adds RCA's and every other connection you need to add amps and stuff. Also if you do that which is the next best thing other then replacing the entire head unit. make sure you get a good amp so that you can tune them properly. you want to do this because the reason why its better to also change the head unit on an aftermarket system is because you can conrtol everything much better and for other reasons but since you want to keep the stock head unit you will have to control them through the amp. alot of info i threw up right now but just trying to save you time and lies that installers will tell you just to get more money. yes it will probably be a little on the expensive side IF you dont cut corners. its up to you what you do but every single time i tried to cut corners it ended up back fiering on me and in the end i ended spending the money pluse some to try to fix things the right way.