If you can’t get enough of trombones (see Berlioz’ Te Deum), you can return in May to Davies Symphony Hall for a celebration of Beethoven's middle years, which includes his rarely performed Equali for four trombones. Also on the program is his Fourth Symphony, the song cycle, An die ferne Geliebte, sung by tenor Michael Fabiano, andAbsolute Jest by the indefatigable John Adams, which incorporates elements of Beethoven's late quartets into the music.