Excerpts from the orchestra's "contemporary" concerts receive a much-needed release. HK Gruber's "Frankenstein" was a curious choice for a program that says it prizes the unknown, since it's been so often recorded. The real attraction is one of the final pieces from composer Elliott Carter, who died months later at the age of 103. "Two Controversies and a Conversation" is, for Carter, a lush and lyrical work: a brief double concerto for a pianist and percussionist. It's not easy listening, of course, but it will surprise those who think Carter was too deep inside his own head.