SiriusXM’s $3.5 billion purchase of Pandora, finalized Feb. 1, will create a digital-radio behemoth with customized radio playlists, a contract with Howard Stern and an estimated 100 million listeners. SiriusXM has a reputation as a tough negotiator, and it has consistently opposed labels’ attempts to raise its royalty rates for recordings, arguing that AM-FM pays nothing to use them.