Philip Glass’ opera Waiting for the Barbarians had “its September 2005 world premiere at Theater Erfurt in Germany, one of the world’s newest and most technically advanced opera houses. When that same production was transferred to the much older Bass Concert Hall in central Texas for its American debut last week, the producers were faced with a technological puzzle. They knew Erfurt’s state-of-the-art, computer-controlled system would need to be replaced with something a little less precise: a bunch of guys perched on beams above the stage.”