The ancient Greek city Sybaris was notorious for the luxurious and sensual excesses of its citizens. Its namesake, the string quintet Sybarite5, which performed at the Barns at Wolf Trap on Friday, prefers to focus on another aspect of the city’s reputation — that “it charmed with music.” Charm and entertain the musicians did with their “Shuffle Effect” program, which allows them to announce from the stage what their iPhone has chosen for them to play next from their current 20-piece tour play-list.