I had the same problem and I had resolved it in this mode (also for HDMI not ARC/eARC and also for Bitstream or PCM protocols): - Configure the ChromecastUltra withthe Android app called "Google Hom...
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I had the same problem and I had resolved it in this mode (also for HDMI not ARC/eARC and also for Bitstream or PCM protocols): - Configure the ChromecastUltra withthe Android app called "Google Home". - in the same app, go to "Device Settings" and set "Surround mode" as "Audio surround AC3/HAC3". - Reboot the Chromecast from menù with 3 dots and play a game to verify...the surround 5.1 will be active now.