I would like to have the Angel’s Vox integration improved

If using the portable version, Audiobook Downloader doesn’t find Angel’s Vox.
You could add the option to enter Angel’s path in the settings of Audiobook Downloader; also add not only “PLay” in Angels’s Vox but also “Add to Angels’s Vox library”.
Also it would be fine to add more audiobook download sites besides Librivox and the option to add URLs manually.