Hot dogs dont quiet much at all. A small Berkley straight through muffler will flow plenty, and actually quiten down the exhaust. It would fit in either mid or rear position, and they cost less than 100 bucks. Why didn't your exhaust shop just put one of them on ?
A picture is worth a thousand words. they wouldn't restrict much, but the fact is the inner tubes are 2 inch, do the maths, 2x2 inch tubes is a reasonable amount less than a 3 inch.
if you are in Adelaide you can have this one for 50.