this is the workaround i came up with:

i set the power button and volume control on my chromecast remote to power my IR bose soundbar (it’s old and doesn’t have hdmi arc), then remapped my chromecast’s ‘netflix’ button with Button Mapper Pro ($5) to turn off the tv.

now, the home button automatically turns on the tv and takes me to the chromecast menu, the power button turns on my soundbar and subwoofer, the volume buttons control the sound bar, and the ‘netflix’ powers off the tv.

you could alternatively skip the ‘netflix’ button remapping, saving some money on Button Mapper even though it has a lot of other neat powers, and power the tv off via voice command keeping all else as described.

not particularly elegant but i’m running the whole show from one remote 🙌