Nice article kerf,thanks.
With the exhaust u could try putting stainless steel wool in there but i have my doubts weather it would work.
If u have the money i bet this Grubee one would be quieter,plus like kerf's article sayes "Longer pipes do, of course, help a bit."..."a little bit of jet assist is also realized."
I'd like to see somebody plumb a car muffler into the system....should be very quiet and not hamper exhaust flow since a car muffler is designed to flow enough for a car engine...try it you might like it! ;-)