There are several aftermarket exhausts that will be louder. None will add any power. Borla, Billy Boat, Corsa, and Akrapovic make exhausts that work. I have not heard it in person, but I've seen a number of Z06 guys rave about the Akrapovic.
For tuning, HP Tuners (HPT) and EFI Live are the two most used tuning packages. They are very robust and take a little time to learn. Predator makes a canned tuning package for the LS2/LS3. I don't know if they do one for the LS7. There are some good shops in FL that do custom tunes if you want to go that route.