Downtown Voices (I sing alto!) and chamber chorus Amor Artis take on a set of monumental works: Frank Martin’s Mass for Double Choir, a deeply spiritual and intricate composition; Thomas Tallis’s Spem in Alium, a 40-part Renaissance motet; and Orazio Benevoli’s Missa Tu es Petrus (for four choirs), featuring opulent Baroque textures and counterpoint. With the Trinity Baroque Orchestra