Box is connected directly to the amp as are the other sources.
I checked the output on the HDMI for the BT box and it was set to surround, yet the amplifier is only receiving 2 channel sound.
Other devices connected directly to the amplifier are working fine, as was the BT box previously.
One factory reset later and it is now functioning correctly again.
You should still have it. What software version are you on (check in settings).
You should be on 31.108.0 / 3.5.136 (although I think the prime app came in on 31.106.0 so you should have it also if you have that).