This is a good week for hearing 20th-century symphonic repertoire, even though the National Symphony Orchestra is on another break. As we approach the first major event of the NSO’s season, the two-week Shostakovich festival in November, we will have the chance Since the NSO Shostakovich festival in November has been cancelled (due to Mstislav Rostropovich’s health problems), this week is our only chance to celebrate the Dmitri Shostakovich centenary some more. MODERN: >> On…