Paul Simon introduced this terrific South African a cappella ensemble when he took us to “Graceland.” That was back in 1985, but the group had already been around for 20 years. LBM has since collaborated with Michael Jackson, Dolly Parton and Josh Groban, among others, and collected five Grammys. Now led by Tommy Shabalala (son of founder Joseph Shabalala), the highly entertaining nine-man group — featuring mostly brothers and cousins — dazzles with their dancing as well as their vocals.