for 64MB cards, theres only CF, and since compact flash cards bring their own ATAPI controler, theres no need for the device to support the size, any CF will fit aslong as the filesystem its formated in is supported by the player
as for SD cards, my D2 is running happily with my 32GB toshiba SDHC card, just remember to use the panasonic SD formatter,
the X-Fi supports it, but the D2 is a better player, and has SD card integration, the X-Fi dosnt, it means you can play from either external or internal memory, but not both at the same time,
as for the clip, theres a small problem of carrying around the converter, another issue is the quality of the connector, its more designed to be inside the battery compartment of a cellphone, not exposed,