Life for the singing monks of Santo Domingo de Silos has never been the same since they became recording stars. Last spring Chant, their Latin-language recording of medieval Gregorian sung prayer, achieved the nearest thing to a record-industry miracle: it ascended to No. 3 on the pop music charts, lodging next to hits by Snoop Doggy Dogg and Nine Inch Nails. Soon the ancient walls of their remote monastery in northern Spain were besieged by tourists and paparazzi. Even more troubling, the monks came to feel that their record company had given them a raw deal.
Though Chant sold 6 million...