What worked out for me to convert AAX files to MP3. When I searched for a solution for this I saw many people had the same problem, so I want to share my solution with them.
Other tutorials just described how to convert directly while playing the audiobook, but that takes way too long. With this method i converted a 2 GB audiobook in about 1 1/2 hour.

Programs:

VirtualCD:
http://www.chip.de/downloads/Virtual-CD_12995223.html

iTunes:
http://www.chip.de/downloads/iTunes-32-Bit_13011021.html (32bit)
http://www.chip.de/downloads/iTunes-64-Bit_35392786.html (64bit)

For those having problems activating /”Sound File Mode/”:
http://www.virtualcd-online.com/vcd/apps/support/Webhelp-EN/index.html?einschalten_des_musikdateimodu.htm

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