When is the sum of the parts of a musical quantity far greater than the whole? When Kelly Willis and Bruce Robison unite as an ongoing musical act. After all, their own individual artistic achievements already sum up to impressive totals. Willis has reigned as a critically acclaimed roots music singer since her recorded debut some two decades ago, and is recognized as a new country and Americana pioneer. Her ever-broadening artistic range and gifts as both a canny writer and interpreter of songs have consistently continued to wow her many fans and music critics alike thanks to her finesse, smarts and irresistible charm. Robison has made his mark as both a writer of indelible smash #1 hits like “Wrapped” (George Strait), “Angry All The Time” (Tim McGraw & Faith Hill) and “Travelin’ Soldier” (Dixie Chicks) and an artist in his own right who boasts a series of eight albums rich with his laconic yet potent grace and emotional dead aim as a songwriter and singer.