Flowmaster Muffler ? 03 Gmc Z71

I have been looking at getting
a new muffler set up, I'm wanting
my truck to be louder...right now
I have one 40s Flowmaster "one in and one
out". Somebody said that I could get a "one
in and two out" and that it would be 2x as loud.
I just wanted to know if this is true before i
go spend 75$ and find out its the same thing that
I already have.:screwy:
Thanks Rob