"In a dim clearing off a county road in Kentucky sits a sagging outdoor stage buried in moss and dead leaves. It used to be the centerpiece of carnival-like Sunday afternoons where local guitarists, fiddlers and mandolin players hammered out old mountain ballads while legends from the dawn of country music performed their classic hits. Most of the musicians who showed up have long since passed, but Nashville stars Ricky Skaggs and Marty Stuart survive....