For a quarter-century, the ten-piece Either/Orchestra has been redefining the mid-size jazz ensemble, incorporating Latin and Ethiopian elements into a group large enough to execute a broad range of compositional effects, but small and nimble enough so that all the players are improvisers and engaged in the act of creation. Based in Massachusets, the group features members from the Dominican Republic, Brazil and the U.S., ranging in age from 21 to 57.