2004 V6 Xpipe; Cats in or out?

Removing any of the emission control equipment is illegal by Federal law.
Having said that, if you do not have emission testing, taking just two off would free up your exhaust a bit without completely killing your back pressure.
It is going to make your exhaust louder and the car will probably throw a check engine light. I'm not sure where the second set of O2 sensors are at. I think they are before the second set of cats...

I just installed a pypes catted xpipe kit from american muscle. The kit came with two high flow cats. On the stock system you have a sensor after the first cat and after the second cat. In my new setup i just have one before and after each cat. other than having to get a new o2 sensor extender it works great. no codes were tripped and i have a nice aggressice but not overwhelming sound. I think i read on here that it is not recommended to go completely catless. as for the stock system as long as you have at lease two with a sensor on each side i dont see a problem.

I run No cats with MIL eliminator(no check engine light) in my DD 04 and love the sound. I just passed the local emission test about a month ago