with all due respect to Jerry C. I would implore you to change out the stock speakers.
I picked up my 07 ST in dec 07, within a week I replaced the stock speakers and head unit. I did the speakers first, it was the biggest jump. in fact, I considered sending the head unit back, I ended up changing the head unit as well, but in my opinion, it did not change the sound that much. When you pull out the oem speakers you will see they look like they were designed in 1985.
ok, that is my 2 cents. good luck.