The Overtone Quartet (clockwise from upper left): Dave Holland, Chris Potter, Eric Harland, Jason MoranJazz supergroups always make me nervous. A promoter or artist assembles an all-star cast of musicians in order to sell tickets, and they generally do, but the music is often lacking. Group improvisation requires everyone to be on the same page, listening to one another. If there are too many cooks in the kitchen, and too many oversized egos, the…