I'm also unable to get Dolby Atmos via BT sport ultimate on my v6 box
Now I'm not sure if that's because we obviously have no live premier league games on at the moment or it's because I've not set my Dolby Atmos soundbar up correctly
I have a Samsung TV with Samsung soundbar both with Dolby Atmos.
I have a HDMI cable from soundbar HDMI 1 to HDMI v6 box and I have a HDMI cable from soundbar HDMI arc to tv HDMI arc and I'm unable to get Dolby Atmos on my TV apps for Netflix, YouTube, Amazon prime and BT sport ultimate on v6 box
Not really as HDMI ARC is for audio from the TV to the sound system, and I don't know the effect of using this to get video in the opposite direction and pushing audio into the soundbar from two sources. Try disconnecting the soundbar from the V6 and connecting the V6 to the TV.