Created in 1998 as an artistic vehicle to showcase young musical talent through the performance of renowned classical compositions, B.A.C.H. is considered in some quarters to be the most versatile classical music assemblage in the Bay Area, with a repertoire ranging from cantatas to masses to symphonies. Tonight it presents its vocal element, the Josquin Singers choral ensemble, in an evening of Advent and Christmas choral music reflecting Western European and Eastern Orthodox liturgical traditions, including Franz Biebl’s Ave Maria and the Cherubic Hymn by Dmitry Bortniansky.