When music director Andris Nelsons opens the 2019-20 season, he’ll be returning to the music of young American composer Eric Nathan, whose vibrant “the space of a door” from 2016 has gained traction with subsequent performances in Louisville and Aspen. (Sample it here.) Nathan’s new work, Concerto for Orchestra, implies virtuosity from every corner. The program also includes a yesteryear commission from 1959-60 – Poulenc’s Gloria for soprano, chorus, and orchestra. Charles Munch led it the first time, with Adele Addison.Nicole Cabell will sing with Nelsons.