This post uses the information gleaned from other posts, I hope it helps.

In order to use Goldwave to convert .aa from Audible files:

1. Uninstall Audible (current version blocks conversions)
2. Install the Win98/ME version (old version, works fine in XP)
3. Uninstall Goldwave 5.x
4. Install Goldwave 5.06 (Google it, I downloaded from Download.com)
5. Open Goldwave
6. Choose All Files (of type)
7. Navigate To Your .aa File
8. Open It
9. Enter Your Username/Password To Activate The File (if required)
10. Watch As It Converts