I've tried to connect an external usb2 hdd via OTG.
It doesn't work.
I suspect a problem of electrical power since the light of the HDD blinds a few seconds, then goes off.
What about a SSD ?
X5 can only provide 450mA current for OTG device. but this is not the problem to support extra HDD, it is a firmware issues.
And what about a SSD ?
Fiio X5 Thread
Check out Duncan's post and the follow up discussion...