Let’s deal with the Sub first. It needs to be bonded with a Sonos device that connects to your TV set, and not a mobile (battery powered) device. Usually, that is a Sonos Ray, a Sonos Beam, or a Sonos Atc (either version). Which of those do you have?

The connecting of the Roam is also problematic. The only way it can receive input is via WiFi (for Sonos music streams) or Bluetooth. Does your TV have a Bluetooth transmitter inside it?

What is a “Sonos SI”?

If you look at the profile of the forum account, I assumed it was a Sonos Roam SL. Took me a bit to figure that out, slightly helped by the tagging on the post, as well.