On Windows Create a Directory Structure:
M:\Audible\AAX
M:\Audible\bin
M:\Audible\MP3
Note that this should not be an SMB share.
On Windows, install AAXToMP3_CS Converter in M:\Import\bin
On Windows, install the Audible Manager
Download Audio Book from Audible to M:\Audible\AAX, make sure you pick Enhanced format (AAX)
Convert
Run AAxToMP3_CS, and pick the AAX File
Select MP3 as the output format
Select the Output Directory as M:\Audible\MP3
Leave all other settings unchanged, and select Convert
Label
Check the MP3 ID3 Tags and filenames, and make sure that the filenames, track numbers and Title tags all sort in the correct order. If not, re-name the files in sequence.
Save
Transfer the completed MP3 files to CDROM for listening to in the car