the Sito is crap, rust quickly and the foot peg mount needs reinforcing, but suspect Jenna won't want another Sito. Not sure what options are out there for a lighter muffler that doesn't come with a tub of Va$eline..
The Pro Duro muffler on mine is very nice quality, stainless steel, not sure of the weight though. Got lucky on Fleebay for about $250, was made to fit a R100GS. Don't think they are available anymore. The mid pipe is large.
Probably have better luck buying a generic muffler and having a midpipe made. The was lots of talk about the stock muffler preforming the best. But who knows with the mukunis??