As the New York Philharmonic opened their stage and their hearts to the displaced musicians of the Louisiana Philharmonic this weekend, Alice Tully Hall became a study in contrasts, with musicians who seemingly have it made in this business sitting side by side with musicians who have seen their world turned upside down. To call the benefit concert, which raised more than $300,000 for the New Orleans ensemble, a triumph would seem to understate the magnitude of the LPO’s plight. But still, for one night in Manhattan, the LPO players could close their eyes and revel in the moment. “It’s bittersweet,” said one LPO violinist. “I’ve lost everything, but I get to play in the New York Philharmonic tonight.”