I suspect that unless you have access to an EEPROM burner & can remove the chip(s) to place them in said device you're pretty well stuffed.
It **might** be that if it can be seen in your PC as a drive that you can shift some sort of software over that will cause the thing to reload the firmware but I doubt it. You'd have to get a sensible response from iRiver about how their devices are initialised during manufacture.