Depends where/what you read, some say that it doesn't need it and the system is pretty much as good as it can be. The grade of stainless on the cat back system is poor though.

Theres not much that can be done to them that will open them up. I've put it on here before, on FFOC someone spent ££££'s on tuning one only to gain something lame like 2.5hp! It had everything, remap, exhaust, pulleys etc..