ETW,
I was at Stillen two days ago, checking out their race FGT. Steve's son Kyle was showing me around and filling me in on the race exhaust and X pipe. Regarding the racing pipes, which mount to the stock exhaust manifolds and replace the stock cats, his comments were the system was EXTREMELY loud. Now, that comment is certainly subjective, and I did not hear the car myself. How it sounds next to the FRPP or similar tubular headers would be a great comparo. Sorry I cannot give you more information than that.
I did purchase the X pipe and bracket that attaches to the rear of the transaxle and set up to have the install done next Wednesday at their Costa Mesa shop. Finally get some real sound (and other related benefits) out of the beast! :banana