In this picture from 2015 you can see the exhaust setup with the X-pipe ahead of the two free-flow catalytic converters. It is hard to see in this picture but the X-pipe have a considerably large opening/flow between the exhaust pipes than it appears on the picture.
If you ask; what is the purpose of the X-pipe? then the simple answer is; the X_pipe actually connects both banks (especially with V engines) of the engine, or more specific in general; the X-pipe balances the flow of the exhaust from each cylinder and therefor it can help with scavenging and increasing the overall flow of the exhaust gases from the engine. X-pipe is somewhat like an equalizer that balances the cylinders exhaust to help by creating a negative wave, for a better flow throughout the exhaust. X-pipes also change the sound of the exhaust. In my case it got deeper at low Rpm´s and raspier at higher Rpm´s.
This picture is possibly better to see the X-pipe; Protection Undercarriage Cover Plates
This is all stainless steel 2,5inc. through out coming from aftermarket headers.
This setup is till the same today in Dec. 2021 and no sign of rust or fatigue.