I'm sure I saw someone recently with that symptom and I can't remember what the problem was. The fact that you're getting *some* sound implies that maybe something isn't tight or maybe one of your switches is set wrong. (I'm still not sure what the switches do, I just blindly copy the instructions.
![Smile :)](./images/smilies/icon_e_smile.gif)
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This probably won't fix it, but you could try looking for "hdmi_audio_96k=1" in the config and set it to 0. It may already be 0. You can leave it there for testing, but once you figure out the problem and get it functional, try setting to 1. If that works, you'll get slightly better sound quality from cores that use weird sampling rates.
edit: Oh, and just in case, you are using a 5V4A power supply for the Mister itself? The default 2A supply isn't enough for many configurations.