soundbar not working with 2 computers

I have a U2515H monitor with attached soundbar and I use this monitor with both my windows pc and macbook pro.  I have both connected (one through displayport and the other through hdmi) and video on both works fine.

The usb from the soundbar is connected to the usb hub on the monitor which in turn connects to the windows pc so the pc sound works perfectly.

I understand that the monitor does not pass sound from hdmi input through to the speaker so I tried connecting the soundbar to my mac with a 3.5" jack cable and it didn't work.  While experimenting to find the issue I discovered that the jack input only works when the windows pc is on as well.  I know the usb ports on the monitor do provide power when the windows pc is off so I can only assume the soundbar depends on drivers to run at all.

Is there any way to get the soundbar to work through 3.5" jack without connecting the usb to the mac?  The cables are going through a really awkward area and I don't want to have to move my desk every time I want to switch between computers.