Can the Mann be something more? A summer venue can dream, and the Mann is having some ambitious visions. Several trends are converging. Commercial music presenters have come into the Philadelphia market in a big way, giving the Mann some competition. At the same time, arts education has become a bigger priority for arts groups and funders, and the Mann, sitting in the middle of a neighborhood, is beginning to imagine becoming a bigger player in education, perhaps even morphing into an urban Tanglewood, with a resident professional orchestra atop a pyramid of training ensembles and master classes.