I’ve spent some time throughout the past month and a half pouring through any documentation I can find relating to the RSE and the audio system and in my search I’ve come up with several things that make me wish I went with an aftermarket RSE over this one. The audio lag is a product of the Bluetooth audio processing through Sync, not the RSE. Connect the monitors to a portable bluetooth speaker and the lip sync is no longer an issue. That being said, I did find out that the video can be delayed to minimize the audio/video sync issues by clicking the three-bar CONTEXT button on the remote, selecting the BLUETOOTH option on the right hand side of the screen and then you can change the video delay in ms. I have mine at 1450ms and it’s about as good as it gets for me. It’s sometimes very slightly delayed, spot on or even a bit fast but a marked improvement nonetheless.
As for building something to pipe audio directly into the amplifier, control the displays from the front and possibly add additional inputs, the RSE is completely contained within the headrests and the only external connections are for power with everything else between the two displays via GMSL so no simple method to gain access to audio or video streams to create a discrete connection between the RSE and amp or enable seeing the menus from the Sync display in the front. Kinda bummed out about that as it’s not going to be a cheap endeavor to get this working how I think it should which is something simple to control from both the front or rear seating positions, something that is easy to get going after stops and something that allows additional inputs to be connected in a hidden and protected low-traffic area of the vehicle.