I had my Banks system get loud. I ordered the MBRP 31" muffler. I installed it where a cat would go, and it fit perfect. You only need 7" clearance (It's 6" diameter).
Now I have near stock volume levels, with a nice rumble on acceleration.
On edit:
And oh yeah, I installed it far enough forward that I can use it when I get my stacks! With only 1 muffler it should calm it down just enough.
I think Tomeygun has the 16" muffler, same design with his stacks.