Can you link the page to that; because I have not found anything in google hardware or cast documentation, stating that the Chromecast Ultra is any different than the other HDMI Chromecasts. Meaning that, they are limited to outputting 24/48 over HDMI. Incoming 24/96 feeds are downsampled.
The Chromecast Audio was the only one to be able to output 24/96 digital via Toslink or by analog with it’s own DAC.