Did you hit the "D-Bass" button on the head unit?
The car I just bought has that radio in it and seemed to "only have front speaker" until I accidently hit the button and nearly gave myself a heart attack when the amp and subs came on. The settings for the speaker fade/bal, and tuning is under the 'sound' button.
And welcome to AF
note - I'm moving the thread to the 'non-performance section. To keep things in catagory.