When Ralph Stanley invited the sold-out crowd at the Paramount Theatre to hold hands and join him in a call-and-response version of "Amazing Grace," few in the audience declined the offer. When else does the average country-music lover have a chance to join in a chorus with Emmylou Harris, Allison Krauss and Union Station, Norman Blake and Patty Loveless, not to mention the stately Stanley? That closing moment was one of many highlights of the Down from the Mountain concert, which brought to life music from the amazingly successful, Grammy-winningO Brother, Where Art Thou? soundtrack. It was an evening of stellar performances from artists both legendary and lesser known. How sweet the sound.