STERN SUES SIRIUS: Howard Stern and his long-time agent Don Buchwald have accused Sirius XM Radio of failing to pay stock awards promised in exchange for boosting the satellite radio company's subscriber levels. In a lawsuit filed in New York State Supreme Court, Stern’s production company One Twelve, Inc., and Buchwald alleged the King of All Media enabled Sirius to surpass its internal subscriber targets by more than 2 million subscribers every year since he went on air in 2006. Howard recently signed a five-year extension with the company that will take him to 2015. (3/23p)