Same thing here. Stadia only seems to support Linear PCM 5.1, which works on my receiver when directly plugged into one of its HDMI ports (and a factory reset of the chromecast), but not when plugged into the TV using ARC.
My receiver doesn't support 4K/60 passthrough nor HDR, so I'm stuck having to choose between 4K+HDR or 5.1 surround until Stadia supports sending our DD+ 5.1 which is supported through ARC.
Given that the audio also has a serious sync issue, I'll stick with 4K+HDR and headphones for now. 😢
Been on with customer support twice now. First time they said they said it was connection, and maybe just plug into amp, and basically all the stuff some says when they have no idea. They said they would "escalate to higher ups" and I'd get a call back that evening. Got nothing.
Second call, the guy said it was game specific and you have to switch it on from within the game. He was then stuck because there was no option in any in game menus.
Now waiting again for a call back which probably won't come.
I did tell them about the many people here with the issue who are getting no assistance and ultimately I would like to make a formal complaint. He told me there was no way to do that unless I wrote a postal letter to Mountain View.
So, great service all round.
Same problem, I've got the first edition I plug directly on my amp Pioneer lx 701 the sound is on 2.0. Like someone else said, I cast a Netflix movie 5.1, get back on Stadia the sound appear on MultiPCM 5.1
But if I reboot Stadia and my amp, the sound come back on stereo every time..
This is strange because at the first time with Stadia the sound was directly on 5.1
Response from Google:
My name is Carlos, one of the Senior Specialist here at Google.
The 5.1 Surround Sound that doesn't work has been escalated already to our team. We're still waiting for a response on how to move forward.
We cannot provide any compensation, if you're unsatisfied with the product you can return it.
I find this to be an underwhelming response and rather flippant - if you don't like it, return it. There was a degree of trust we placed in Google when we pre-ordered and it should not be dismissed. If I was a prospective customer considering buying into Stadia right now, and I saw this then there is no way I would make the purchase.