To deepen the tone you will need to deal with what Bill said, the front manifold is really restrictive. I've ported a few and trust me, they are not good stock.
Changing the front and the down pipe will change the tone. Installing a free flow cat will deepen it more. And I believe you have 2 mufflers on your car, so installing either a flowmaster or magnaflow series 40 muffler will give it a nice tone. Installing rockers or a cam will finish off the sound. Purplehaizer has a nice tone with his. Here'* mine but I'm running a single series 80 so the tone would be slightly different.