I’m using surround sound at home for the first time. I think on some 2.0 video content an attempt is being made to upmix to 5.1 or similar somewhere in my chain of devices but it’s patchy and I would personally rather just have my left and right Era 300s also playing the L and R channels. Is this possible, either through Sonos or from particular devices? I’d consider buying a replacement streaming box that does this. 

AppleTV4K ——> LG C4 —(eARC)—> Sonos Arc Ultra/Era 300s/SubMini

This is what I’m currently using.