Although I have no personal experience with this quite yet. I asked an objectively similar question on my thread in the link below, there's alot of good advice there.
http://www.impalaforums.com/chevy-impala-7th-gen-discussion/1501514-dual-exhaust-help.html
http://www.impalaforums.com/chevy-impala-7th-gen-discussion/1501514-dual-exhaust-help.html