There's nothing like sheer virtuosity in instantly relatable music to liven up the proceedings. In the weekend's Benedict Music Tent highlights, saxophonist Steven Banks brought a high-voltage jolt to Friday's Chamber Symphony with a new, crowd-pleasing concerto written for him. Then on Sunday, violinist Gil Shaham and the Festival Orchestra reveled in Eric Korngold's ear-soothing, frankly Romantic concerto, which Jascha Heifetz debuted in 1947.