I replaced the stock speakers in the stock door panels and dash (base model without the Bose audio set-up) for better sound for the music I listen to.
I added a small 8" sub located in the rear hatch area along with a amp and signal processor. The signal processor has time delay along with controlling the various speakers crossovers (i.e. active set-up) between the front (mid-bass & tweeters) and the sub. Check out the DIYMA web site for additional reviews.
P.S. I found in best to listen to various speakers in the stock 370Z location if at all possible in order to decide on the best speakers that sound good to you!
My set-up is posted in this forum if your interested.