Complex sentence: He raised their reputation to one of the world's leading ensembles, and with them gave world premieres of sixDmitri Shostakovich symphonies: numbers 5,6,8,9,10 and 12.
Split into simpler sentences: He raised their reputation to one of the world's leading ensembles. He gave world premieres of six Dmitri Shostakovich symphonies: numbers 5,6,8,9,10 and 12.