U2515H with soundbar (AC511) - how to get sound from HDMI input to soundbar???

I have the U2515H monitor with the AC511 soundbar.

I have an Apple TV and a PS4 connected via HDMI.

I thought the sound would just come out of the soundbar but no luck.

So I thought if I get a 3.5mm audio cable to connect the line-out from the monitor to the line-in to the soundbar, then it would work, but still no luck.

I'm guessing that HDMI audio is digital and the line-out from monitor and line-in from soundbar is analog.

Is that the problem? or is there a problem with the monitor or soundbar?

Thanks.