Last May, Jonas Kaufmann and Camilla Nyland, aided and abetted by the Boston Symphony Orchestra under the baton of Andris Nelsons, set the Wagnerian world aflame with concert readings of Act Two of Tristan und Isolde, Wagner’s paean to forbidden love. Now Kaufmann tackles the agonizing hour-long death scene for Tristan that constitutes the bulk of Act Three—a tour de force that Isolde, Emily Magee on this occasion, has been known to upstage with the eight or so minutes of her transcendent Liebestod. Based on Kaufmann’s showing last year, that’s not likely to happen this time. At the peak of his powers, the most versatile tenor of his generation has yet to tackle Tristan in its entirety, or to perform any of it in the theater. On-fire act-by-act teasers are well and good, but the time is fast approaching for the full Monty. —M.G.