Billionaire investor Daniel Loeb's proposal to separate Sony Corp.'s movie, music and TV businesses would give the Tokyo-based company a chance to join the 3 1/2-year media rally it has missed. Loeb, founder of Third Point LLC, yesterday recommended selling as much as 20 percent of Sony's entertainment unit in an initial public offering that would free it from the struggling electronics business. As an independent company, the maker of "Spider-Man" movies would benefit from more disciplined management, investor attention and fatter profits, giving a $6.1 billion lift to Sony's market value, he wrote in a letter to Chief Executive Officer Kazuo Hirai.