AC511 USB Soundbar, functionality

Hi, not sure if right place but here we go..

Just bought the AC511 soundbar and would like to know if there's a way how to hear audio without it or the monitor being connected to the pc or laptop. Basically I have an 32" DELL monitor that I want to be using as a TV in my gym, so have the chromecast plugged into the HDMI port, the audio out 3.5" jack plugged into the soundbar but can't get the sound.. if I plug the usb cable from the soundbar to the laptop the sound works fine, but I don't want to have the laptop there..

Any ideas..?