Are composing and conducting compatible activities? In the 1980s, when his career as a podium whiz began to skyrocket, the budding symphonist Esa-Pekka Salonen put composing on the back burner. Lately, he has struck a happier balance. Centerpieces of this program are his own Castor and Pollux, two pieces originally conceived as one, inspired by the mythic Greek twins, one human, one a demigod. —M.G.