First thing to check is if your TV will allow the optical output to work simultaneously to the HDMI-ARC. If it will then just connect the Resound to the optical and leave the soundbar as it is.
If not then get an HDMI-ARC audio extractor like this one. https://www.zuummedia.com/product-p/hha-a-4k.htm
Connect it in between the HDMI-ARC port on the TV and the soundbar HDMI input. Connect the Resend to the audio output of the extractor.
You may need to change the audio output of the TV to pcm.