With its bold new brand of acoustic music, Joy Kills Sorrow pushes right through the envelope and out the other side. The Boston-based stringband brings a decidedly modern sensibility to an old-world sound, channeling the prodigious talents of its individual members into elegant arrangements and well-crafted songs. While the group pays due homage to its Bluegrass roots—its name is taken from WJKS, a radio station that broadcasted the Monroe brothers’