It would be easy to transfer binary via automatic writing with something like this:
Then the binary can easily be converted to text (ASCII).
The postmaterial person (spirit) doesn't even need to know the equivalences beforehand, the medium can just print a page with all the Binary->ASCII equivalences for the postmaterial person to see.
I think binary should be the standard when trying to transfer information from the other side, trying to transfer audio or video is like building a house starting by the roof instead of the foundations.
The SoulPhone project will probably break that barrier in this decade.