I would think that where your problem lies is in the piping itself. I do believe that most Z's Ive heard with a 2.25 inch system do not sound well at all, not to mention that if you piping is press bent, then you really have about a 1.87 inch exhaust at the bends.

That would make it sound well less then desirable.

I will say that a flowmaster will give you the "sound" you are looking for but it wont give you a performance advantage.

In all my applications before I have found that dynomax mufflers sound the best, at least in my opinion.

Good luck !

im curious about that set up you have there. Can u get a sound file of the exahust? id like to hear it with that combination.

http://media.putfile.com/TwicePipesExhuastShortDriveBy

http://media.putfile.com/280zTwicePipesExhuast

Those are some video's of my exhuast setup =)

well my old Twice Pipes exhuast setup

FWIW, I went with the MSA 6-1 coated headers also. To that I went with a custom bent 2 1/2" pipe, a resonator next to the driveshaft and a flowmaster exhaust. At idle it sounds like it has a V-8. I love it.