Not having looked underneath, but I presume that as the exhaust manifolds go into a Y piece and through the same catalyst, whatever comes out of the tail pipes should be the same on both sides - yes?
The two manifolds with pre cats go into the main Y piece with the main cat, this single pipe then goes to the center box where it splits to two again just in front the box the two pipe go through one box and out to the two tail pipes.
