Under the hood it says california and federal, so if I get new cats I can't just get federal correct? People tell me that the car would drive poorly and the check engine light would come on if I didn't get the exact pair. Even if I don't live in california I still have to get cats that meet californias' standards? Those cats cost so much more and harder to find. Anyone have advice? I live out in Pa and I have a 4.2 a6 2001. Thanks in advance