Board Thread:Lore Discussion/@comment-209.7.3.188-20160303204000/@comment-26893431-20160511211107

Ashley Kirshbaum wrote: if there are other ways of learning the voice, then it clearly is not "only accessible to a select few who get chosen"

also, him learning it from Nahfahlaar is nothing but speculation.

There's no recorded other way of learning the Voice.

Still more likely than finding another way, judging on the lore we have.