So if the 360 box is connected directly to the TV make sure it's not connected to the HDMI-ARC connector on the TV, setting the 360 Audio to follow content should be the best but you could also try the PCM settings.
Welcome to the Community and thank you for posting.
I am very sorry to hear you are experiencing issues with the sound on your 360 box.
Can you please confirm if you have been able to check the connection and settings as suggested by roy247? If so did this help?
If not, please do let us know and we will be happy to assist further.