That’s not how that would work at all. The copyright of a derivative work has no effect on the existing copyright of an underlying work.

If you record yourself reading a book, you own the audio recording copyright but it would be a copyright violation to reproduce that copy without a license for the underlying rights.

In this situation:

If the AI generates the audio recording of a book, no one owns the copyright of the audio recording but it would still be a copyright violation to reproduce that copy without the underlying rights.