If possible, I would run one set of omnis overhead with a spacing 1/3rd (or less) of the total spread of the musicians and a height about the same distance as the mic spread (or a little more). If that is not possible, then I would do the same thing from the front of the stage. In addition, a stage lip (or onstage) MS pair (M being card or subcard). I would not use blumlein, too risky, if the acoustics aren't perfect, it will sound bad...very difficult outdoors. Let us know how it comes out!