It all depends how much money you want to drop into sound.
For a really affordable upgrade that is the best bang for buck - Get a set of 4 new speakers.
If you are wanting some low end, a 10 or 12 inch sub, amp and a low level line converter is needed to give you the bass, but speaker replacement is definitely needed.
If you are looking to spend $1000 or more, only then would I suggest even considering to replace the stereo head unit. It is a very good quality unit, compared to even a few years ago where replacing the head unit would get you the best bang for buck. This is not the case with the 2011+'s. In fact, the speakers they provide are so crap, I would suggest almost throwing them away.
2012 Black 3.7L =Performance Package