Here is a simple hack to explore the firmware of the pmp. It does not require you to open up your pmp and modify anything, nor flash any peice of hardware.
Download this file and place it in the /iRiverSys/etc folder. Now goto the file brower, and switch views.
Now on to figure out howto read bits of the /proc folder in the text editor...
(the secret is opening up this file, and changing the path from /mnt/Root/bla to /mnt/Root/../../)