OK, I misunderstood what you were trying to do.
I am not familiar with that file type.
I try to recommend freeware when possible and easier ways of doing things.
There may well be a free alternative to payware, if it were me, I would look for one.
Some payware is also bloatware.
I copied this online...likely the way I would do it.
You will need to convert the .aa to something usable like wav.
"Aa files are a proprietary audio format used by Audible to sell various audio books on their website. Converting these files to WAV is not easy, but it can be done by using a program to record the playback of an aa file directly from the sound card of your computer so there is virtually no quality loss. Make sure you give yourself enough time for the conversion because it will take as long as the duration of the audio file."
Good luck, it is a proprietary file.