Only two years old, New Jersey-based MidAtlantic Opera is mounting an ambitious concert this Saturday night at Manhattan's august music temple, Carnegie Hall. Its modest goal: world peace. [...] "Music and diplomacy are interestingly tied together," says Tramm, "and the creative impulse that's necessary to make art and music is a similar — if not the same — creative impulse to communicate and try to get along. Music is a natural form of diplomacy."