I personally would not modify the performance of a naturally aspirated Subaru. I would do aftermarket wheels, coilovers, and paint, but no more. You don't want your Subaru to sound like a rice rocket and have nothing to show for it. However, if you really want SOMETHING done to your exhaust, just look up a part called a resonator. Cat-back exhaust is too big of an investment IMO for a Subaru that is not an STi or a WRX. Websites like CarID can check the compatibility of certain parts. Some are also universal.