Hi, I have tried the OTG function with USB sticks and with 3 powered hard disks (500GB, 1TB and 2TB and 3 different brands). Only the USB sticks work.
OTG is not intended for hard disks apparently, and when I asked FiiO they said it was impossible to support them.
I hope they will be supported in future somehow but it doesn't look likely or imminent.
It's also not wifi enabled. It essentially plays from Micro SD cards and USB sticks (or acts as a USB DAC for such as a laptop)
No problem! Here's a 1TB USB stick - http://www.amazon.com/Kingston-DataTraveler-Predator-1TB-DTHXP30/dp/B00E65QM8O - Only a thousand bucks!
Did you try the external drives that are powered by USB? I have a 500gb external drive that only uses a USB wire.. I will give that a shot and see (I think I need to update my firmware before using the USB OTG, though)