Miro Magloire's New Chamber Ballet collaborates once again with the Ekmeles vocal ensemble in the world premiere of Magloire's "Sanctum," set to instrumental and vocal music by two major contemporary composers: Kaija Saariaho and Karin Rehnqvist.   Singers Charlotte Mundy, Mary Mackenzie and Elisa Sutherland join NCB's resident musicians, pianist Melody Fader and violinist Doori Na.   Dancers are Sarah Atkins, Elizabeth Brown, Kristy Butler, Amber Neff, Rachele Perla and Madeleine Williams.