A Transcendent Voice By ARTHUR LUBOW Thomas Quasthoff titled both his autobiography and a recent CD compilation “The Voice,” underscoring the bass-baritone vocal instrument that has made him an internationally acclaimed singer. But it is safe to say that the main thing an audience notices when Quasthoff takes the stage is the body in which that instrument is housed. He stands just over 4 feet 4 inches tall, on stumpy legs without knee joints or much thigh. His hands (missing two fingers on the left and one on the right) emerge from his shoulders like flippers. He lurches and sways...