I can't find it, but somewhere in this thread or perhaps another HM-801 thread, I recall reading where someone found a maximum number of files, but maybe that was total number of files in a single folder. I don't know. In any case, if it works for you but not for me (except when the 64GB card is far from full), my unit must be defective. The list of "limitations" just keeps getting longer, while the clock ticks on my ability to return it under their 30-day policy.
My biggest problem at the moment is that I've found workarounds for all the most annoying issues and have actually started to enjoy the music! Which, as I'm sure it has done to many other HM-801 owners, pacifies me into inaction. To one degree or another, we've all learned to "enable" these handicapped machines, lowering our expectations, just to have access to the good sound.