In the Stadia menu it shows that I am getting 5.1 surround sound. However only 2.1 channels are active. I'm guessing it's because my older stereo only has Optical and analog in and my Sony Bravia TV only has optical out. Both XboxOne S and my PS4 Pro support Bitstream audio, hopefully Stadia will too someday. It is older tech however so it probably won't happen.
I'm having the same issue. Google please give us b it stream so we don't have to invest in a completely new setup. I just got mine and it's a bummer I can't use stadia with it...
In order for 5.1 to work with your setup @DaniGamePlayer , both your receiver / soundbar and your TV BOTH need to have eARC. This is relatively new technology. Unfortunately if you have a device older than about a year, you are out of luck. If either have the standard ARC, you will not get 5.1