If all you're doing is upgrading the speakers, you'll be wasting your money. I have yet to hear of a stock head unit and amp pushing new speakers to their potential. You'll here "some" improvement, but it'll start distorting more when you try to turn it up loud. You'd actually be better going with an amp first. BUT, you can only push stock speakers so far. Unless you're an stickler, the head unit will be okay. Except you won't be able to do any fine tuning. For that you will need to add a crossover/eq between the head unit and the amp. At least a 10 band. Then you have the amp. Best bang for the buck (and ease on installation) get a 5-channel amp. If you upgrade the speaker, get components. Any well-known speakers will do. You can leave the sub but don't expect too much. You can either just replace the speakers inside the enclosure, or have one made. Basically it all depends on your wallet. You don't have to spend $2k on a better than stock system. Especially since you don't have Nav, you may as well replace the head unit. Best thing to do is shop on Ebay. You can get everything you need for about 30-50% cheaper than at the store. Then go to a shop that will install it for you. Shop around though. Some will charge you through the nose because you didn't buy it through them. But it's still cheaper. Good luck. I have Nav so I haven't quite decided on if I want to lose some of the other features that comes with it besides audio.