The string quartet lives, and in the JACK Quartet, who make a welcome repeat visit, it lives with exhilarating intensity. John Cage is represented at a moment of strange serenity, just before he started dealing out the wild cards of indeterminacy. In contrast, the quartets by Aaron Cassidy and Horatiu Radulescu work at the limits of what musicians and instruments can attain. Cassidy, an American based in England, has worked closely with these players to remake the quartet sound. From Radulescu, whose music made a huge impression here three seasons back, we hear his extraordinary fifth quartet, subtitled “before the universe was born.”