Note that I reviewed the X5 on 1.00; things might change during and after international release. I suggest you do the change for only a few first, then see how it goes before doing the rest.
Also, I suggest the combination of Everything and Bulk Rename Utility (Everything to search for all such jpg files; BRU to rename them at one go) if you really have to change all that filenames :) I cannot find any Mac/Linux alternatives unfortunately; maybe someone here can help with that? :o
Sorry, should have quoted you too since you asked about this too...
Thanks for your help!
Hopefully the FiiO support team can give confirmation on this issue.