According to Talkers Magazine, Glenn Beck radio show pulls in 9+ million to Levin's 6.25+ million. Add Beck's 3+ million on TV (which is unprecedented in cable news)and his audience does dwarf Levin's.
http://talkers.com/online/?p=71
According to this Beck is #3 behind Rush and Sean and Levin is tied in 4th place with Ingraham and Savage.