I suppose you are talking about the following, right?
At minute 05:33:
Will the Android harness then pass through the optical connection to the HeadUnit to keep original functionality?
How is the audio quality? People reported bad audio quality through Aux, but this seems to work differently. I guess what I am trying to figure out is if this will 100% have OEM audio quality as I retrofitted a different/better AMP and don't want to lose the quality.