HiFiMan-801limited to SDHC, correct?

The HM-801 can only use SDHC.  I would stick to genuine class 4 Kingston cards, but you can check here for other cards that have been reported to work.  This post may also have some useful general info. about the HM-801.

maybe the player can use if the firmware is support and the driver of player understand  exFAT filesystem

From Wikipedia:

In the 3.0 specification, the electronic interface of SDHC and SDXC cards is the same. This means that SDHC hosts which have drivers which recognize the newly used capability bits, and have operating system software which understands the exFAT filesystem, are compatible with SDXC cards. The decision to label cards with a capacity greater than 32GB as SDXC and to use a different filesystem is due solely to the limitations in creating larger filesystems in certain versions of Microsoft Windows. Other operating system kernels, such as Linux, make no distinction between SDHC and SDXC cards, as long as the card contains a compatible filesystem.

SDHC and SDXC cards and hosts have these compatibility issues:

• Existing SDHC hosts will only support the SDXC cards at up to UHS104 speeds;^[38]
• SDXC hosts are backward compatible with SD and SDHC memory cards.^[53]
• The operating systems that currently support SDXC are: Linux (with a proprietary driver for the exFAT filesystem^[54]), Microsoft Windows 7, Windows Vista SP1+,^[53] Windows XP SP2 or SP3 with KB955704,^[55] Windows Server 2008 SP1+, Windows Server 2003 SP2 or SP3 with KB955704, Windows CE 6+, and Mac OS X Snow Leopard (Intel-based