I usually do this by hand with surprisingly good results: I use calibre to convert the ePub to txt and then fix some common problems (i.e. remove line breaks an

I usually do this by hand with surprisingly good results: I use calibre to convert the ePub to txt and then fix some common problems (i.e. remove line breaks and page numbers) using regular expressions. Then I convert it to an audio file using the macOS Automator text-to-speech action (be sure to download the high quality voices first).