Avi Stein's admirable early-music celebration returns for four nights at St. Paul's, offering a distinctive program each night. The Sept 11 program, "The Grand Overture," explores orchestral suites by Bach and various contemporaries. "Café Zimmerman," on Sept 12, offers chamber music by Bach, Handel and others. Pieces by Rameau, Marais and Clérambault dominate the "Concert Spirituel" set on Sept 13. And Bach cantatas ring out the festival on the afternoon of Sept 14.