An unusual instrumentation, the string sextet offers listeners a depth of sound and a wealth of texture unlike any other instrumental grouping. CMS presents in “Sensational Strings” two such works, one by beloved composer Antonín Dvořák alongside one by 20th-century master Erwin Schulhoff, both containing rigorous technical demands and emotional depth; add to this Beethoven’s Quintet for Strings in C minor, a shocking sensation in its day, and listeners will be astounded by what an unconventional grouping of strings, in the hands of the best chamber musicians of today, can do.