Gemini Air audio surround issues, big zero

I have the P21KW-500 (appears to be an ATT-branded chromecast) dongle direct into a new Denon X4800H AVR via HDMI, obviously. The issue is when trying to use Dolby audio.  When Dolby is enabled on the dongle, the audio level is very low, like 20-25 dB below stereo content. The AVR will report the incoming audio as 5.1 PCM and it shows all 7 speakers as active, however, the rear surround heights have no audio with any of the upmixers (I'm guessing that has to do with the container). The Gemini will show that DTS, DTS-HD, and Dobly TrueHD are incompatible which is untrue as this AVR decodes everything. As soon as you try to make a change in the advanced audio settings of the Gemini, surround is shut off and it reverts to 2 ch stereo PCM. 2 ch PCM is lame even with the upmixers engaged. It's not the AVR as the Samsung tv speaker audio level is also very low (with the AVR in standby, passing through the gemini A/V)

PQ is great with the 4:2:2: chroma subsampling, HDR, and 12-bit color (my panel is 4K120 and 12-bit), but the surround implementation for home theatres on this dongle is a complete fail. 

I also have a chromecast with the DTV app and the audio works as expected with all the codecs functioning properly, however the UI is clunky and PQ is not as good. 

So what's the solution for this lame a** surround audio??