I was told only 32 but maybe something changed. I know others tried larger cards at one point and had problems with them. Could have been a software update that I missed that had that option but I watch that thread.
Edit--
From owner manual:
Introducing, the HiFiMAN.The HiFiMAN, is a new, state of the art design music listening device, for the most discerning music listener, which incorporates a high quality flash based transport,which uses a state of the art 16bit 48kHz digital to analog converter (DAC), customer swappable amplifier to cater to any customer's tastes, along with a user replaceable rechargeable 18 volt battery, which allows the user to carry around a musical library with as many 32 GB Secure Digital HC cards as required, for an endless supply of lossy to lossless music files. The possibilities are endless.