For more than 50 years, the Kronos Quartet has provided the answer to the question, “I don’t know much about classical music—where should I start?” Unlike many traditional chamber music outfits, the Kronos crew—currently longtime mainstays David Harrington (violin), John Sherba (violin) and Hank Dutt (viola), with more recent addition Sunny Yang (cello)—is determinedly progressive and…