I'll be synical here, BUT IMO I don't think anyone in your audience would notice or even care if your sound was bright, dull, mellow, or anything. They are going to like it no matter what! For example I was djing some house music one night and for the last record I put in some supertramp. Now, this is TOTALLY different than what I was playing before... but did anyone look up? No, they just kept on talking and drinking! Things would be different if you were playing in a room full of music teachers, jazz professionals, or classical buffs, but I don't think the regular people would notice that much. as for different mouthpieces, try a bunch of them out... who knows maybe those dreaded selmer 80's (or whatever they are) would work great in your situation!

Gotta commend chiamac on bringing out the Supertramp! As far which mouthpiece, it sounds like you're looking for a piece that can cross over from jazz to legit. Don't worry too much about how your sound is perceived as long as it blends well with the ensemble you are playing in. I've recently gotten some modern Otto Link NY mpcs and I'm falling in love with them very quickly. Links never floated my boat in the past, but I had to try the NY on account of the huge chamber and concave sidewalls - which warms the sound considerably. You could use a 5 or 5* facing as a cross-over piece - using harder reeds for mellower tone. I play my 5* with a Medium Hard Fibracell for more subdued playing. The 6* and 8* come out for other purposes...