You may have misunderstood, I use the 360 remote and that controls the soundbar volume through the TV, the 360 is only paired to the TV.
I don't think there is a easy way of unpairing something to delete it from the 360's history, so what are the problems you have with the 360 paired to the soundbar you have only said that the 360 is controlling the volume, as you haven't said does it still control the volume if you set the volume keys control to your TV or do you want to connect something else.