I upgraded my sons base V6, we put pioneer TS-D6802R front and rears. I used an alpine KTP-445U in line 45W 4 channel amp which fits in the recess under the head unit to amplify both sets of speakers. It also will allow you to set crossover and you will get good sound from both front and rears. MTX loaded thunderform sub in the trunk which comes with amp and sub and wiring. System sounds great for less than $700
I have started down this same path with the installation of the KTP-445U and Alpine 6832cf speakers in the doors. I have another set for the rear deck, but I am thinking I may purchase a set of adapters that will allow me to use a set of 6x9's and leave it at that. The improvement in sound just replacing the door speakers and fading to mostly front with a little bit of fill from the factory rears is amazing. Can't recommend this option enough for those wanting to keep the budget below $500.
ALSO: I used the Miccus Mini-Jack RX Bluetooth
receiver in the 3.5 jack to wirefree the connection to my iphone. Since I have Pandora and GPS app on the I phone it makes a great system. The only issue is that the power point in the console is hot all the time and the Miccus needs to be re-powered to link to "last used bluetooth connection". But if I wire a power point to a switch controlled power source I can overcome the necessary unplug-plug sequence currently required when I get into the car.
2014 Race Red Base Model-3.7L, MT82, Tech Package, 18" Black Factory Wheels, AirRaid CAI