Arthur Arnold made his conducting debut with the visiting Moscow Symphony Orchestra in 2001 at Amsterdam’s prestigious Concertgebouw, where the conductor famously descends through the audience on a staircase from the balcony level, then through the orchestra and over to the podium, surrounded by applause and anticipation. It was an extraordinary moment for Mr. Arnold, who, as a 14-year-old, had snuck into the same hall – darkened – and stood on the podium, dreaming of this.