I think that you should be able to point your DAW that will open raw files at your usb connected iriver and open the file this way...
You will be asked the format of the file (16 bit/44.1k/stereo) and then it will open the file, next do a file save as saving to your computer.
This has worked for me in the past when the wav header was not written properly. If this doesn't work, search here for file recovery utilities dealing with iriver.
Good luck,
Joe