Welcome to the forum! Just Running 3/8 inch conduit from the mufflers out put all the way to the back.[Easy stuff to bend] Will cut noise way down it will cut some power Though. Do something along those lines with two mufflers and a little bigger pipe. You'd be surprised. It will be as quite as a little honda generator.
Here is what our search engine brought up. Seams a bunch of reading to weed through though. [sorry]
Others will soon pipe in!
quite muffler - Google Search