How to quiet down my 3" exhaust?

I think a second muffler would help, but you already have a second muffler in place. I dont think the change from the glasspacks to another turbo will be very dramatic.
Come to think of it, an acquaintance had a pair of large mufflers (in his case, only one pair) installed under the trunk where the gas tank used to be in his demon. It was a fairly quiet, smallblock stroker, 9second streetcar.