hello MJWRX03 . IMO, the cobb ss tbe with optional high flow car is real nice. one cat on the wrx is plenty. But it is not neccesary. The stage 2 map will delete the cel's associated with map and tbe. In Pa if the OBDII test passed (no cels!) then the car will pass. No sniff test and no visual. Well thats how it is were i live.
hope that helps alittle. Cobb website has some info to.
let me know if theres anything else.