Guest conductor Asher Fisch, who led the BSO on Saturday evening, has long been a champion of Dorman’s work. This busy and ultimately conservative Double Concerto was a star vehicle for its soloists: the married duo of violinist Pinchas Zukerman and cellist Amanda Forsyth, longtime partners in both performance and life. With her robust timbre and earthy accents set against his silvery sound, which was ethereal without being silky, they played with obvious relish, and sounded more at ease with the piece than the orchestra did. After intermission, Zukerman again joined the BSO for Beethoven’s stately Romance No. 1 in G, dispatching tart and tight phrases with a few sour notes.