Alfa Ebooks Manager contains built-in audiobook player for MP3 and M4B files, so you can use it to listen to your audio books.
All parts of each audio book should be attached to the same book card. You can add them manually in the Book card -> Files tab, merge in Scan or merge parts into single books after Scan (using Merge Books icon).
You can start playing audio book from the right-click menu. Audio player shows you audio book files and allows to sort them by track#, title or duration.
You can use the familiar controls to pause, stop, rewind and toggle audio books.