To open the Boston Symphony Orchestra's 2013-14 subscription season, revered German-born conductor Christoph von Dohnányi is joined by violinist Augustin Hadelich in his BSO subscription series debut and cellist Alban Gerhardt for Johannes Brahms's Double Concerto for violin, cello, and orchestra, the composer's final orchestra work. Brahms's Symphony No. 2 dates from the previous decade. Composed relatively quickly after the composer's long-awaited First, the lilting No. 2 is generally regarded as the most genial and relaxed of Brahms's four works in the genre.