Daniel Barenboim returns to the Proms, this time as both conductor and soloist, taking the piano part in Beethoven鈥檚 Triple Concerto. Schoenberg鈥檚 Chamber Symphony startled audiences with its ruthless concision 鈥� a reaction against the excesses of the late-Romantics. But excess gets the last word, in Tchaikovsky鈥檚 Fourth Symphony, the musical expression of some of its composer鈥檚 most-troubled and heartfelt emotions.