I did some testing and managed to get the speaker dock to work. Initially, it wasn't working but I played a video coming through the tablet speakers, removed the tablet from the dock while still playing the video, reattached the tablet to the dock and the audio automatically switched from the tablet to the dock.

Exiting the apps, restarting them while docked, and the audio continues to work through the dock.

If I restart the tablet while docked, playing a video has the sound coming from the tablet. Removing and redocking, gets the audio to come from the dock.

I was digging through the settings and if you look at Settings > Sound > Dock speaker plays, the default is Media audio only, but you can set to All Audio.

    5 months later

    brawfx So I got a tablet recently on sale and the dock speakers worked fine for a few days, then today I tried to play something on the dock speakers and for the life of me it will not work.

    I do not see any settings under Sound that dictate what audio the dock plays, but I do have the "docking sounds" toggle at the bottom, so it knows it is the tablet.

    I've reset the dock with the button on the bottom, rebooted the tablet, seated/unseated it numerous times, tried different media sources, and zilcho.

    The dock plays the boot up sounds and everything so I don't believe the speaker went bad or anything like that.

      Sometimes the tablet gets confused or there's a process that's delayed in GOS that recognizes the dock if no sound is coming out. If you're playing sounds while docked and it's coming out of the tablet speakers, simply re-dock it and the sound should come out of the dock.

      I have the best success if sound is coming out of the tablet when I dock it.

        Kottonballs yeah it seems no combination of docking/playing media/undocking seems to get the sound to come out of the dock.

        Can you verify on the latest GOS release that you have an option under Sound settings of which audio the dock outputs? Because I see no such option at all.

        I see a Docking Sounds setting (on/off) regardless of dock status. I'm on the latest stable build.

        a month later

        archvile77 I just checked again, and that setting is gone for me as well. If I put the tablet on the dock and play music, it comes out of the tablet. If it let the audio continue to play and remove and redock, it switches to dock audio. So it's buggy/clumsy, but there is a way to get it working.

          brawfx yeah it seems no matter what I do, I can't get audio to come out of the dock. I've tried different audio sources, rebooting everything, using the dock reset button on the bottom. I'm out of ideas. I know the dock works because if I reboot it or reset it, it plays the little startup jingle. For whatever reason, the tablet just refuses to connect to it for audio. Charges just fine. Frustrating.

          Well, after I posted that I tried to search around the forum again, and one post suggested the USB peripherals setting. Sure enough, I had mine to completely block USB peripherals. Changed it to allow and the damn dock speakers work now. Never would have guessed it treats it as a USB peripheral. Would also explain why they worked at first, and then I would have changed that setting later on. Son of a gun, this just made my day!

            3 months later

            Perhaps a warning promt in USB settings on the Pixel tablet when people want to block USB peripherals would help prevent confusion. (After all, the four-pin connectors on the speaker don't come to most peoples' mind when thinking about USB ports)
            "Disallowing USB peripherals will also stop the docking station from emitting sound" (or something like that)
            Not sure if that is possible though.
            Perhaps we could ask the developers of GrapheneOS.

            The USB peripherals setting will be gone from all Tensor devices (6th gen and up) soon, since the USB-C port setting obsoletes it. It doesn't currently cover the tablet's pins, so it shouldn't come up unless the pins are special-cased in the future.

              matchboxbananasynergy Ah, that is good news! It was indeed slightly confusing to have these two options next to each other, thanks for the reply!

              4 months later

              I have a somewhat related question. I want to start testing GrapheneOS and the tablet seems like a great test bed rather than my daily Pixel 8. Does the Cast features still work with GOS with the Tablet? Like can I use it to cast from my phone to the tablet etc?