Hello from Sweden.
This question does not only involve Infuse on my Apple TV with latest update tvOS 26.3. But audio handling in general.
I read several topics on downmixing to stereo but I want ask anyway. I have an Apple TV4k latest version connected to my LG OLED C2 from 2022. I don’t have a soundbar or AVR so I use an optical cable to my DAC ( Chord qutest for hifi music listening and occasional films) . The DAC only accepts 2 channel PCM so I have to downmix any multichannel content.
One way is to let my TV do the down mixing. I set the audio to Auto on my Apple TV and digital audio out on my TV to PCM to my DAC. I then get multichannel LPCM on Infuse. And Dolby Atmos on Netflix for instance on my TV as expected.
The other way is to set my hdmi input not to bitstream but to PCM that will make my Apple TV to downmix multichannel audio. It will make sound different but not necessarily better in my opinion.
There is a setting in the audio settings on my Apple TV to choose Stereo. Will there in that case be any difference to change to it from auto? I read in a thread somewhere that Apple TV only uses the 3 front channels when letting the Apple TV doing the down mixing. Can this be true?