The wav files downloaded from http://www.brutaldeluxe.fr/projects/cassettes/index.html are loaded into my Apple IIe from my MacBook. Output from earphone jack to input port on back of IIe. In put port on back of IIe is the one closest to the joystick connect port. I had to keep the volume high on the player on the MacBook for this to work. It worked on a number of wav files. Others not so much. Here are a few.
Cassettes – Loaded to Apple IIe from Audio output on MacBook