At the end of SmithAmundsen LLC’s annual partners retreat last month, Larry A. Schechtman flexed his vocal cords. That involved a performance by a band called Mid-Life Crisis with Schechtman, the firm’s managing partner, singing lead vocals. “To lighten things up, we decided to form a band with four partners and a nephew of one of the partners who plays lead guitar and is a real musician,” said Schechtman, whose previous singing efforts involved karaoke and belting out Harry Chapin songs at a …