I assume that you can't boot rockbox can you?
You tried to flash an iriver official firmware or a patched one with rockbox?
If you can boot to rockbox you could flash your unit with a Rockbox only bootloader.
Then you could reflash the OF, but I don't see a reason to.
Summarizing, if you can't start Rockbox, or you can't get the original firmware at the point where you can upgrade again then sadly you should forget it.
As Llorean said the unit is ruined, it can be brought to life again only by special equipment.
