Mahler’s imposing Symphony No. 6—which he completed in 1904, the same year that Ravinia was founded—is in itself a full evening’s worth of music, not just because of its enormous scale, but because it is such profound music. The work is a perfect vehicle for the Ravinia debut of Dutch conductor Jaap van Zweden, music director of the Dallas Symphony Orchestra, which he is credited as having brought to a new level of artistic achievement.