You could think of them as the Monkees of a capella music. Street Corner Symphony, the group that took second place on NBC’s “The Sing Off,” didn’t exist for long before the show: The band was formed in order to compete on the television vocal competition. Since its almost-victory, the band has worked with the likes of Ben Folds (a show judge), Claude McKnight and Allison Krauss. Trivia note: Five of the six members of the group are sons of ministers. Details here.