I was planning to pick up the Flowmaster or Borla catback exhaust since they do come stainless, but learning that there is a difference between the Calmini SC and non-SC model just further confuses me. The extra part that the Calmini-SC, what does it do? And would it really matter much, that the Flowmaster and Borla model may or may not have specific models for a Xterra SC? Any input would be appreciated. Thanks....