Also, I had to dig around to find out how to change the BOOT SCREEN:
While HU is on, hold down eject + SRC, then hit the reset button (this causes a reboot).. continue holding the eject+SRC down during this reboot, until a screen pops up saying "Kenwood" or "OEM" once this is displayed you can release it.
Select OEM, select your USB drive, navigate to the file, select it, hit enter. (takes a while to load to memory)
Then hit SRC to power down. I think I had to hit eject+SRC again for it to stop showing the option to pick other backgrounds.
Here's the BOOT SCREEN: (used something different for boot, than normal operation)
Some earlier models require 16-bit bitmap (.bmp) files. I found his out when helping someone with their custom Mercedes logo recently.