Could you also share the HDMI360 apk they sent you in case anyone needs it in future?
If it were me I would be tempted to try a (very) temporary fix (not with solder) to check if bridging those 2 sets of pins fixes the issue. If it does give audio then I'd hand my unit in to a local repair shop that I'm familiar with as that's too small a fix for my DIY soldering kit and my skills.
It's a dedicated apk for playing the HDMI in source. They finally sent him it (he confirms a few posts ago). You can see in the video the app is named HDMI1.