ARC is for passing audio 'to' the sound bar from the sources connected to the TV. use a regular HDMI port (check to be sure port is 4k capable if you have a 4k set top box).
I now have an optical cable connected from the x1 box out to the receiver. So now the x1 box is connected by HDMI to my receiver and optical cable from x1 to my receiver.
Still no sound when the receiver is turned on. It's passing the signal through to the tv and tv plays audio from its internal speakers but nothing I do can get Comcast source audio through my receiver speakers
you would need to consult your receiver owner's manual. note that modern receivers do not need the optical path as the HDMI cable is carrying digital audio along with video to the receiver.