No, I tried without the changes. To no avail.
If the iRiver is doing nothing the screen is 'clean', so to speak. Whenever it tries to do something, i.e. spin the disk up or highlighting the next object in the filelist the screen becomes unreadable because of the distortion which manifests itself in random colored lines on screen. The displayed colors are all present in the screen that is supposed to be displayed.
Those setting I mentioned worked to prevent that. I know mine is a pretty severe case, but it worked.
To be clear, this is not Rockbox's fault, since the player (h320) has the same problem (be it less severe) with the later, video enabled, versions of the original firmware.