When great musicians push themselves to do something different, it can be an exciting prospect. Christian McBride's New Jawn is a great example of that. And when those musicians really enjoy that challenge, that's when the magic of jazz happens. After a pair of successful trio albums and a Grammy-winning big band release a year ago, McBride's latest outfit is pianoless. In the tradition of similar bands, such as Ornette Coleman's two-horns-bass-and-drums quartet, the lack of chordal instruments