Chamber music has always been the ultimate “insider” experience for classical music aficionados. But the form’s always limited audiences have been declining in recent years, leading some to rethink the way small-scale concert music is prepared and presented. “A small group of musicians playing in an intimate setting is, after all, one of the most popular forms of music making today. You can find ‘chamber music,’ by this definition, in bars and clubs across the country on any given night. But those invested in maintaining traditions — including some presenters and commendably passionate audiences — want a more conservative definition that keeps out the innovation.”