In this May 12, 2014, file photo, Paul Singer, founder and CEO of hedge fund Elliott Management Corporation, speaks at the Manhattan Institute for Policy event in New York. Prominent athenahealth investor Elliott Management Corp. is offering about $6.5 billion to take the medical billing software maker private after saying it has grown frustrated with the company's performance. The investor says it owns about a 9 percent stake in athenahealth, and the company has not made the changes it needs to grow and create value as a public company.