Well, perhaps we do hear from Nihilus in one form. I think the DS male voice on the website belongs to him. Its a very brutal voice, I recognize it to be the narrator from Jonathan Glazer's acclaimed black and white Guinness adverts. Perhaps it may be Sion's, but the voice sounds somewhat synthesized, as if from behind a mask for example. And I always presumed the male voice of the trailer to be Sion's.