OK, my suggestion would be to get something like this:

https://www.amazon.com/Digital-Coaxial-Optical-Converter-Bi-Directional/dp/B07VHPJ1DD

This will convert the digital audio output on your TV (which is right next to the RF/antenna connector) from using coax cable to an optical cable which can plug into your soundbar.

The TV should take the audio signal from literally any source (using any connector on your TV that supports audio), convert it to digital if necessary, and pass it through the coaxial output. It would then be converted by the converter box into an optical signal and fed into the soundbar.

You should be able to hook the SNES up this way with just the usual A/V cables, let the TV do the work of sending the audio to the converter box and on into the soundbar.