i would say check out
clubgp.com If you are interested in ANYTHING 3800 series engines, it is there, granted the forum is for grand prixs, but we use the same engine, so a lot of the performance parts and exhaust stuff will be the same. AT the very least you can check out the exhast section to see vids of other members setup's so you can see what sounds best to you......but a personal FYI from someone with a 3.8, beware the dreaded DRONE with custom exhaust, i dont mind so much, but i can be troublesome at times