Update: We did it! 
Developing Organizational and Managerial Wisdom – 2nd Edition (Audio plus text version)
The audio files sizes were too big to host inside of the Pressbook, so we hosted the files in our newly-created Open Educational Resource (OER) Content Kaltura channel. We embedded the full playlist for an uninterrupted experience, as well as embedding individual audio files into each chapter.
We were able to make the individual files available for download, but unfortunately weren’t able to find a way to mass-download all of the files.
I look forward to encouraging more of our faculty members to consider creating audiobook versions, and now that we’ve done one we can begin looking at ways to improve the process.