Try Pair remote with devices > Change audio set up and just select any make which should clear your currently chosen soundbar (if you've chosen one)
Following that click on Volume Keys control and set that to your TV instead.
You could then pair it up with the current soundbar again if you wanted to
Your soundbar may also have a CEC option which allows other devices to turn it on, you could turn that off instead.
You can also turn off One Power on your 360 which should stop the surround sound receiver turning on, although this will also prevent the 360 from turning on/off your TV.