Hello, Just installed an AVIC-8400NEX. Everything seems to function, but I don't understand what I can display on my rear seat screen. I have my head unit connected via iData maestro to retain OEM functionality, including the rear seat entertainment screen. I can get DVDs in the HU to play on rear screen (so wiring is correct). And, I get that HDMI won't work due to security unless I use an HDMI-RCA cable (bummer). My question is about the Mirroring function. I have set AV/Rear to mirror but the screen remains blank no matter what's on the HU. I thought this would mirror, say, HD radio o