If you format the card to FAT32 or NTSF, than the Prime should be able to read it. The easiest way to format would be to just put the card into a PC and use Windows to format it.
Re: Response: Transformer Prime- 64gb card and Wi-Fi?
The question I have is whether the firmware will recognize sdxc cards. This question applies both to the micro slot on the tablet, itself, and to the full size slot on the keyboard dock. Is it really as simple as proper formatting?