This question has gone around before... I think the stock sound system is better than average but still not impressive. The bass, to me, is bloated and thrummy, like they're trying to impress. I replaced all speakers with Focal and added McIntosh head unit and amp. I'm using an Alpine sub amp for the rear "subs". The little Focal sub drivers are pretty impressive for their size. The amps and crossovers are in the rear fender wells - plenty of room in there.

While I was at it, I added sound absorbing material inside all panels - huge amount of work.

I also added a Sirius satellite system but canceled it because of the poor sound quality - sounded like good AM.

NOTE to those interested in satellite: the antenna will go under the dash and work well. Remove the dash panel where the 2nd airbag switch is to access that area.