For some of us, autumn brings with it the pleasures of baked goods, homemade soups, colored leaves, moody skies, carved pumpkins, black-and-white horror movies, used book shopping, sweaters, Brahms, and cozy cups of tea. But for the House of Atreus, “fall” meant something completely different. It’s comedy tomorrow, tragedy tonight, with music inspired by Aeschylus’ “The Oresteia” by Darius Milhaud and Sophocles’ “Elektra” by Alphons Diepenbrock. That first step’s a doozy, this Sunday at 10 pm.