On Valentine’s Day weekend, in four cities, three members of the American Bach Soloists presented a chamber music performance of great variety, including music by such contrasting composers as François Couperin, Heinrich Biber, J.S. Bach, and Arcangelo Corelli. The program selections were a bit disjointed for my taste to say the least, but in the concert I heard Sunday at St. Mark’s Lutheran Church in San Francisco the performers managed to tie things together well enough, balancing fireworks with remarkable poise and an elegant intimacy.