I just got an LG OLED48B49LA and since the internal speakers are really bad, I would like to use my two Sonos Five Speakers with it.

This used to work fine with the old TV (plus Apple TV) I had before, as it had a chinch output, so I could connect the TV to the Five speaker through 3,5mm and could control the volume with the Apple TV remote.

The new TV does not have that, it only has optical and HDMI Arc.
I bought an Optical-Chinch Adapter, which works fine but obviously I can’t control the volume of the speakers with the LG TV remote.

This is my question: what options do I have to be able to control the volume of my speakers with the TV remote?

Any adapters, any other products to buy that aren’t too expensive? 
I would like to avoid buying a Sonos Arc for now. 

Thanks for taking time, I really appreciate it.