Jimi,
First, it was nice to see you and your friends at the show the other day.
Second, I don't know exactly how to describe the difference but I'll give it a go. The cup shape seems to have a slightly difference in the way it slopes to the throat. It ALMOST seems like a double cup effect. As for the general cup shape perhaps it is a little more bowl shaped. Those are just my limited visual perceptions. You would really have to ask Dave about what other manner of "gourd shaking" he does. As you well know, what his mouthpieces look like have a lot less to do with how well they work than some of the other voodoo he puts into them.
ML