To make the exhaust louder, you would need different mufflers. catalytics and resonators really only change some of the higher tones and normally add "raspyness," to an exhaust.
How about thinking of an e-cutout added in before the mufflers?
Also if I look here:
http://www.vividracing.com/catalog/m...-p-104611.html
It says this:
Meisterschaft GTC exhaust systems include electronically controlled exhaust valves, allowing the end user to control the overall tone of the exhaust. Closed valves offer the quietest sound, while full open valves will showcase the loudness of a truely open exhaust. The valves can be set anywhere in between to get any unique combination of sporty or loud.
Do you have this? Can you leave it open?