Getting Google Cast on my Soundbar

I have a Samsung Q800A soundbar. It ships with built-in support for the Apple Airplay protocol, but I’m not really an Apple kind of guy so that’s never been particularly helpful for me. So, instead, I have a Chromecast Audio plugged into it via TOSLINK, and that works fine - except for the fact that there’s no way to explicitly pick TOSLINK as the audio input. Instead, there’s a “Digital In” option that refers to both the optical in and eARC input from a TV. Not inherently a problem, given I’m unlikely to be watching TV while listening to music, but my TV is a Samsung Frame, a device that’s intended to display art whenever someone is standing nearby, and which infuriatingly generates an eARC signal even if it’s only in art mode and isn’t going to make any noise. This switches the soundbar away from optical and I get sad. I could plug a video cast device into the HDMI port on the soundbar and cast audio to that, but then the art would get replaced with album covers whenever I’m playing…