One of the most astonishing records of 2019 has slipped under many radars, likely because it’s hard to describe, categorize, and explain. Seven years in the making, the composer William Brittelle’s Spiritual America was co-released in May by the venerable Nonesuch Records and New Amsterdam, the new-music label that Brittelle cofounded. It features dozens of musicians, including the Brooklyn Youth Choir, New York’s protean Metropolis Ensemble, and Durham’s Wye Oak.