I've recently added a couple of posts in the BE forum and PE thread about audio files from a subreddit called GoneWildAudio. I learned of this resource from a post in the stories forum on Futanari Palace.
More searching there has turned up these two contributions, both of which seem to be recordings of the same script.
The Hazards of Demon Summoning (Futa TF, femdom... etc.) Listener has summoned a demon for some sex; but the demon is too powerful and has its way with him. Futa TF happens about halfway through. The reader has a very suitable British accent. There's a part 2 to this, but it doesn't seem to include any more TF or growth so I'm not really interested.
Kokonyoe-Demon-Futa-Enhanced This is another reader's enhanced version of just the TF part (i.e. the good part) of a different recording of the same script, with added sound effects. He posted it in the comments under the original
full recording -- but that seems to have been deleted along with the rest of the recordings by that contributor.