THEY BE ILLIN': "You could say we're a pop group," says Il Divo's Carlos Marin. From left are Marin, Sebastien Izambard, David Miller and Urs Buhler.A PREVIEW: A Il Divo A When: 7:30 p.m. Monday, July 6. Where: Cleveland State Univesity's Wolstein Center, 2000 Prospect Ave., Cleveland.