Is the firmware of the chromecast and the TV up to date?
Ah, ok. Didn´t see, don´t know why, that you are using this switch. I don´t think this switch can work in this constellation. The input of the chromecast is missing to the 5557.
Which LG TV is it? Does it have an optical audio output?
Remove the switch and plug in an optical cable directly from the TV to the sound bar.
The TV can´t be used via HDMI to be an input to the switch. It´s not a splitter.