It would be easy to attribute the early success of Potato Moon, an acoustic bluegrass-rooted group, to the trickle down of the Grammy-winning, platinum-selling O Brother, Where Art Thou? soundtrack. But that theory fails to take into account the band's pre-Brother beginnings -- and the beverages of local coffee house the Hi-Hat, the main outlet former employee and Potato Moon cofounder Barclay Martin used to sell the group's self-titled debut disc, which blew through an initial pressing of 1,000 copies. (The disc had a title before the group did; Martin and guitarist and singer Ben Stancil, who met in Liverpool, England, several years ago, have decided simply to name their act after the album.) Thanks to good coffee, regular customers and Martin's charm behind the counter, buyers discovered a midsummer night's dream of a disc -- somehow both quaint and haunting. Martin, who plays banjo and guitar and sings, describes Moon's folky sound as "contemporary old-time." Now a sextet with two new female voices (Stancil's sisters; their father has also joined), Potato Moon returns to KC after a summer of practicing and playing in the Stancils' hometown of Grand Rapids, Michigan, for its first local performance. The group has also lined up recording dates for its second album, a project worth anticipating.