When rebuilding my side pipes, I placed a modified Harley/Davidson exhaust baffle just before the turnout. At the time, there were different models of the baffle, don't recall the specific one I used.
The mufflers are the 427 Corvette side pipe mufflers, heavily modified.
At the front end used, the Car Chemistry 3 disc exhaust inserts. Reduced the size of the hole in the center tube.
Car Chemistry Exhaust Inserts - SummitRacing.com
With the set up, significant sound reduction was the top priority, accepting in advance what ever power loss there would be. My Z06 with a Bassani X pipe and the Borla Quad Stinger Exhaust is louder during acceleration etc.