Fabio Luisi is the music director of the Dallas Symphony Orchestra, but his C.V. also includes seven seasons conducting the magisterial Met Opera Orchestra. Contemplating the financial hardship of so many orchestral players, Luisi and the DSO president, Kim Noltemy, thought, Why not invite the Met musicians, many of whom Luisi knows well, down to Dallas? And so they did. In a symbol of solidarity, a blended orchestra of 100 DSO and Met Opera musicians performs Mahler’s Symphony No. 1, sometimes called “Titan.” The work, much revised by Mahler, began as a “symphonic poem in two sections” and drew from influences literary and pictorial. Eventually the composer suppressed the detailed program, leaving us with the four movements we hear today. —L.J.