Most classical music fans would quickly recognize the Paganini theme that Rachmaninoff expanded into one of the most familiar piano concert-pieces in the repertoire. But most listeners have probably never considered what actually goes on in a theme-and-variations, where one composer’s singular idea is transformed into a wide-ranging and free-flowing work, yet without ever straying too far from the original thought. Rachmaninoff penned 24 variations on that Paganini theme, and Michael Barnes has taken the daring step of actually explaining each one in an American newspaper. The Pop Culture Enforcement Squad is presumably making its way to Austin to deal with Mr. Barnes.