Cutting-edge Chicago chamber sextet eighth blackbird teams with Will Oldham, a.k.a. Bonnie "Prince" Billy, one of his generation's most profound and eccentric singer-songwriters, to perform the Frederic Rzewski’s spoken-word piece, Coming Together, plus arrangements of songs by Oldham and Bryce Dessner. Opening is the tandem of gentle guitar maverick Bill Frisell and avant-folk singer and banjoist Sam Amidon, a potent-on-paper pairing that lives up to its promise and then some.