In the Chromecast world, there are basically two categories of audio support: devices that report a “supports high res audio” flag and those that don’t. The ones that support high res (Chromecast Audio) will output up to 24/96 out of their digital outputs. All other devices (ie: the Home series of speakers and all the Google Chromecast devices with HDMI output) only go up to 48kHz. In the case that you supply either category of device with audio that exceeds the maximum supported sample rate, they will just downsample (by successively halving the sample rate) to a rate that they support.
Also, at least in the devices that we used for testing, TVs with “Chromecast built-in” functionality output at 48kHz, no matter what.