Here’s a group we don’t hear that much about: The Olmos Ensemble, created byfour talented and experienced musicians: Eric Gratz (violin), Matthew Cohen (viola), Julian Schwartz (cello) and IlyaShterenberg (clarinet). They will perform two concerts in the upcoming days: “Music From St.Mark’s Presents Olmos Ensemble” on March 9, and “Olmos Ensemble presents Viennese Masters,” on March 10. The first concert …