does that mean I need to reconnect the sound bar from the TV via optical?
I think we need to get back to the basic's here, assuming you only watch TV via the 360 then the ideal configuration would be the 360 connected to the soundbar and then soundbar to TV using HDMI, connecting to a non arc HDMI connector on the TV.
You can then connect the TV to the soundbar using optical for when you watch something on the TV to feed the sound to the soundbar. The downside on this is if you watch say netflix on the TV as an example you will probably lose dolby 5.1 to the soundbar thats why they use HDMI-ARC from the TV to soundbar as most optical cable connections only support 2 channel stereo.
What HDMI connection's does your soundbar have, better still what model TV and soudbar do you have.