I'm pretty sure your installer needs to hook the subs up where the rear speakers would be hooked up. I also had mine installed by a BB installer (not at best buy). My installer did not want to attempt to find and hook up the wire that goes to the headlamp switch (that tells what display to use). I might attempt it myself but its not that big of a deal.

My advice, don't mess with it unless you know what you are doing. Take it back to best buy and tell them to fix it.