Looks and sounds great, what's the purpose of the X section just after the CAT's???
To answer your question, this has a scavenging affect and when the exhaust pulse from any of the cylinders on the left bank passes through the X pipe it creates suction down the right side manifold thus pulling exhaust fumes out, until a pulls from that bank comes to do the opposite for the other.
These are quite common on V8, V10, V12s, but I assume due to cost reasons they dont install them on V6s.
The X30XE is the perfect candidate for one since its firing order is 1-2-3-4-5-6 and the 1-3-5 are on the left and the 2-4-6 are on the right.
Having drive the car now for 2 weeks at various conditions, i can say with certainty that it changed the power curve on the engine, its increased in some areas and smoothed out in others, much like what polishing the upper intake area did for it.