New-music nerds of a certain age will remember Crumb’s haunting García Lorca song cycle Ancient Voices of Children or his anti-Vietnam War piece for “electric string quartet,” Black Angels. They may have been weird, but they were cool. Now the grand old man of the American avant-garde at age 87, Crumb is still composing away – most recently, Metamorphoses Book I, a cycle of piano works based on his favorite paintings. Avant-garde diva Margaret Leng Tan gave the premiere in D.C. on May 7, and David Patrick Stearns was there.