The orange pi doesn't do HDR properly. Linux in general doesn't support it natively, and the hardware doesn't provide for it.

On most devices Dolby Vision, etc get downgraded or support only the streaming profiles (profile 5) . If you want full Atmos, Dolby Vision, etc you have to buy one of only a handful of devices. The Vero V is one of them. There are only a few others.

https://osmc.tv/wiki/vero-v/dolby-vision-support/

Does the optical out actually transcode to 5.1 or is it only proper optical when the source has DD built in ?