I know this subject came up recently but I don't think anyone posted what exact universal Magnaflow cat they used. I am trying to determine which ones to buy to install into my existing track pipe (2.5"). Magnaflow told me to buy one that has one inlet pipe--which clearly won't work for the M5 which has two 2" pipes exiting the y-pipe. Pretty damn trick exhaust for a stocker. Anyway, it appears their 9000 series stainless would work but I am just not sure. They haven't replied to my latest email which included a picture of my stock cat to make my point.