If by "low key" you mean stock looking or near, then, from what I've seen, Borla's catback is the closest looking to stock out there. I have head sound clips of the Borla on our cars and it does sound really good.
Do a search on here for "Borla" or "Greddy" or "Magnaflow". Those seem to be the more popular choices. Although, Greddy's catback is far from "low key" looking.
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