Yea, you might want to hit up Daytona on the forums for a bit of knowledge on that subject. He has a pretty full on system now. The stock cats take out a huuuuge amount of rasp in the exhaust note. He's got 2 high flow cats, 2 hotdogs after those and 2 more resonators on the main section. It's still quite loud and would probably drone a fair bit on an auto.
Also what year was your car first registered? If it's 2010 or later then you can't de-cat it.