We have a Roku premiere 3920eu connected to a Dolby atmos, DTS HD capable amp, but only seem to get Dolby Surround Or DD + at best whereas when I stream the same programs via my Smart Blu ray player I get better sound formats - For instance Netflix - The Sandman immediately defaults to Dolby Atmos on my Sony Blu-ray player, but on the Roku the only option is 5.1 - I have checked all connections and menu options and am at a loss - no support whatsoever from Roku - they clearly only care about flogging their Kit rather than offering a proper support function! Has anyone got any suggestions ?
From a list on the Wikipedia Roku page, the 3920 should support HDR10 and Atmos. But, different apps can be finicky. There is a thread for the Premiere/Ultra models with many very knowledgeable people, and apps can one day work properly, then they update and something breaks, and then another update fixes it. Roku doesn't have any real control over that. Even other non-Roku devices can work or not work depending on various updates.
https://www.avsforum.com/threads/official-roku-4k-hdr-premiere-ultra-owners-thread.2604017/page-985