I’d been watching and listening for a good mesmerizing minute to the second selection in this “Brilliant Cover Songs” series when I tapped the pause button and went back to the beginning to confirm what had suddenly dawned on me just the moment before: Were these guys really creating this seeming symphony of sound without employing any instrument other than their gloriously blended human voices? Sure enough—the four members of the Dallas-based “Kings Return” only sound like they have the backing of multiple instruments and/or a robust choir as they create a lush musical soundscape powered only by voices that traverse…