To be completely honest, I don't think such a conversation could be explained by the concept of a voice, or even words, even if it is in the manga.
If anyone has ever had a mild psychedelic experience (with no sensory hallucinations), then I think you know what I'm relating to. I think a communication with a being on a higher plane, or in a higher consciousness, real or not (but the experience of it is real, at least we know that) is almost a telepathic one, but SO MUCH MORE complete than communication with words. I understand it sounds very stupid expressed like this, but just take my word for it. And that's basically how I imagined the communication with the IoE in the deleted episode.. it's very hard to try to relate that type of communication to what a regular human consciousness experiences, but I would say it would be like sending thoughts to eachother, instead of using strange sounds or words to represent the thoughts.