Audible audiobook is protected with DRM encryption is AA/AAX/M4B/M4P format,if you want to play purchased Audible audiobook on Sonos, MP3, iPod nano, Android devices or other non-Apple devices,you must to convert purchased Audiobooks to MP3.
What you need is an Apple Music Converter,which also is an AudioBook Converter for Mac is designed to remove DRM from iTunes Audiobooks and convert them to popular formats such as MP3, AAC, AC3, AIFF, AU, FLAC, M4A, M4R, and MKA, and then, users can play their purchased Audiobooks on various devices. Also you can choose to save ID tags and metadata information to the output MP3 and M4A files or keep Chapter information in the converted M4A files.
Step 1: Import audiobook to the software and Select Audiobooks
Step 2: Determine output formats - MP3
Step 3: Select Output Folder (optional)
Step 4：Customize output filename (optional)
Step 5: Convert purchased iTunes Audiobooks to MP3
Read More: How to Convert Audible AA/AAX Audiobooks to MP3