I installed my avh-p8400bh today along with a rocker switch. Flip the rocker on, off, on. After that, I was prompted on the screen to click ok and the I was able to see the DVD menu. Before toggling the rocker switch, I could hear the DVD menu music looping in the background. If I didn't already have the switch bank, I'd probably have gone another route. For $2.49, the rocker was a sure fire winner for me. If it hadn't of worked, I wasn't out much.
As a side note, my rocker switch is in my center console, hidden. I have a bank of switches so adding another one wasn't a big deal to me (I have a 5 gang bank and have two spaces left. One will be used to toggle the rear camera once I get that ordered (I want to be able to see my load behind my truck).
I found the icon on the screen to turn the rear camera on so I might not install a switch - although flipping a toggle switch is fewer clicks than what is required to turn in the camera straight from the HU so well see.