Audio Testing
Audio performance is good on the ASRock X299 Extreme4, although I think the overall output volume over the back ports could be a bit higher. The audio circuit isn't completely isolated from the rest of the board here, and a look at ASRock's X299-ITX/ac motherboard showed that a non-isolated audio design can perform amazingly well, too.
RMAA results are below. Considering everything, this is a good result, but we have seen better.
RightMark Audio Analyzer