When playing Amazon Music Unlimited Dolby Atmos tracks through my Arc/sub/One SLs the volume level is ridiculously low. It doesn't happen with HD and Ultra HD tracks. Looked around and found this reddit post:
Tested the suggested workaround of simply pausing the Dolby Atmos track and restarting and it automatically fixes the volume every time. Crazy and annoying. But it avoids the problem of manually increasing the volume of an Atmos track only to have the next non-Atmos track blow you out of your chair.