“Midway through the world premiere of Nathan Davis’s macrocosmic masterpiece, “The Sand Reckoner,” the word “myriad” melted in the air of Seiji Ozawa Hall, layering and tessellating in six voices on a text by Archimedes. It seemed to shake off its semantic meaning, dissolve into pure sound, and re-assemble itself into its form. Myriad were the styles, myriad were the sounds, and myriad were the discoveries at Tanglewood’s Festival of Contemporary Music kickoff concert. “The Sand Reckoner” was the greatest of these discoveries. The texts married math and poetry across the centuries, with selections from a Middle English Bible and William Blake (the latter sung by the balmy-voiced mezzo-soprano Katherine Beck) interspersed between busy passages of Archimedes. The six singers were uniformly excellent, and gritty electronics lashed against a delicate celeste played by one of the festival’s curators, International Contemporary Ensemble’s Jacob Greenberg. Here was music of spheres, both as tiny as a grain of sand and as large as a world.”