Sorry to be pest, I'm having the same issue with no sound. I have the OEM rear screen, the sound was working, there was a small pop sound from the speakers and now no sound. The MOST has the green comms link flashing slowly which I'm told means the link is down. The amp under the passenger seat seems fine, which leads me to believe it's the rear screen board has gone bad.
Did you bridge the pins at the screen end of the connector? If so, would you be able to take a photo of which pins on the connector. I tried the suggested pins, but still no luck, not sure if I'm reading it wrong or I'm just too dense to figure it out.
Thank you kindly.