I actually have a small breakout board here but haven't got around to putting my project together.

Basically, I have a SONOS BEAM which is attached to the ceiling by the projector screen, the BEAM accepts optical via a dongle which imitates a ARC endpoint, however, running optical from the projector to the beam is not entirely feasible, and because it's mounted o the ceiling the channels are swapped.

Currently I solve this problem using a raspberry pi and a hifiberry to pipe the bluetooth sound, but I'd prefer for the audio to come from a HDMI source (Nvidia shield).

This makes the whole thing a bit of a mess.

My plan is to take the HDMI output from the shield (I have obtained the HDMI specs) and then inject the digital audio into the beam directly by pretending to be an ARC device, this will allow me to also swap the left and right.

I did the preliminary work on faking an ARC endpoint (both as the source and the sink), I just haven't had the time to sit down and do the actual real work device.