Scored for soloists, mixed chorus, children’s chorus and chamber ensemble, Iannis Xenakis’ music for Oresteia has been cited as “ruggedly dissonant” since its 1987 première in Sicily. A wooden-planked stage is empty save three platforms, one each for the chamber players and percussion, another for a drummer on a separate perch. On a high screen to start, a loop video shows an almost-naked woman stretched out face down in a bathtub who is being hosed down uninterruptedly with water. No forewarning, and the clip changes to a thick forest, a small girl being physically abused by an adult man. While the same video images reappear at the end of the opera, but it’s nebulous soft-edged shapes –mood landscapes as it were – that are the usual backdrop for the 90-minute piece.