Rv6 or xlr8 j pipe? And more questions

So my bro bough an 08 tl type s.

Eventually he will be wanting to mod the car and I know the exhaust on these cars is very restrictive.

I understand there is the rv6 j pipe and the xlr8 j pipe. Both eliminate the third car... Is this ok? Will it cause a cel or will he not pass emissions?

If he stays with the stock pre cats and removes the third one at the end is that ok? Cause my car only has one cat which is a high flow and it passes emissions.

Thanks guys