Bach’s dazzling explorations of counterpoint (composing with two or more simultaneous melodies) share the stage with innovative works by Eastern European masters. Szymanowski’s String Quartet No. 2 explores new tonalities, colors, and levels of expression—including some melodies and rhythms inspired by Southern Polish folk tunes. Dvorák’s quartet is a bold late work with an opening theme built from brief motifs, a gorgeous songlike Adagio, a quirky viola and cello duet in its penultimate movement, and a lusty finale.