(Written by: James Bash) OrpheusPDX, a new company founded by Christopher Mattaliano in Portland, Oregon, concluded its second season with a brilliant and thought-provoking production of Nico Muhly’s “Dark Sisters,” at Lincoln Hall on August 24. “Dark Sisters” explores and exposes relationships in a polygamous sect and reveals the courage of one sister-wife to leave it. With Stephen Karam’s libretto {…}