It sounds like that you have Anynet enabled. Disable Anynet and that should do the trick. If you'd like more detailed instructions, please reply with your model codes for both models.
My sound bar works great, but it wants to "auto tune" if you will to ARC. It is connected with an HDMI directly to the TV. Is there a setting that can be changed so the source doesn't have to be adjusted to HDMI instead of ARC. Sometimes it has to be changed 3 or 4 times before it sticks.