I think Windows can format FAT only up to 32 GB (but access - read and write - also larger FAT-formatted devices). For formatting a device with more than 32 GB FAT under Windows, you will need an extra (freeware) tool. FAT itself goes up to 16 TB per device in theory.

Why are they implementing two microSD slots into one device instead of one (or two) SDXC slot?   microSD is currently at 64GB each, SDXC at 256GB.   SD will always be more than twice the capacity of microSD.   I have about 600GB of APE files and it seems there is no audiophile DAP...