Controlling sound base with Siri remote

Hi,

Not strictly related to Kodi, but isn’t all part of my setup.

I managed to pick up a cheap Sony HT-XT100 sound base without a remote control. I’d like to be able to control the volume with my Siri remote on my Apple TV 4. Now, if I had the Sony remote, the Siri remote could (probably) learn from it. But I don’t!

Does anyone know of a workaround to sort this?

Best wishes,

Mark