I have my Calibre library backed up to a 32GB micro-SD card, and my library contains many file formats for each book (ePub, mobi, AZW3, AZW). Is there a specific file structure that the Aura HD requires, or one that is most optimal, for reading books from the SD card? It seems to me that maybe I should only have my ePub books on the SD card if I want to read from it on the Aura HD?
