Comento que se trata de los archivos que guarda la aplicación de Apple iBooks Author, para crear contenidos, en un formato parecido al EPUB, para tabletas iPad.
Digital book created by iBooks Author, a program used to created iBooks for the Apple iPad; saves the chapters, sections, and pages of the book, as well as the page layout information; also saves the book's title, introduction media, table of contents, and glossary; used for textbooks, picture books, multimedia books, and many other types of digital books.
iBook Author documents can be exported to the .IBOOKS format for direct upload to an iPad (through the iTunes software) or for sharing with others. IBA files can also be exported to .PDF or .TXT (plain text) files for reading on the local computer or other devices.
IBA files are saved in a compressed .ZIP format. Therefore, you can open them manually with any Zip decompression program to see the book contents.
Si buscas alguna aplicación de Adobe compatible, que abra o visualice estos archivos, o que pueda editarlos y mantener el formato, la respuesta (hasta donde yo sé) es: ninguna.