Singer-songwriter Rufus Wainwright has become a darling of the indie-rock scene over the past few years, renowned for his poetic lyrics and the “plaintive vibrato” of his voice. But Wainwright’s musical tastes might surprise most of his fans: he’s a major opera buff, a serious fanatic “who can trace the seamless structure of the banquet scene from Verdi’s Macbeth and discuss the subtleties of Gluck’s lesser-known Armide.” And don’t think Rufus’s obsession with the music of Europe’s cultural elite sat well with his ’60s-era folksinger parents, either…