Since you already have the Tannoy FX speakers, you might as well go for it. Use the Kef for the normal 5.1 arrangement. Add the Tannoy as back speakers to make it 7.1 and Atmos speakers for 7.1.2. If your room is on the smaller side, this will definitely help create a complete sound envelope for movies with an Atmos soundtrack.
Neither of the Kef or Tannoy bass module are a true subwoofer. But again, since you have them, you might as well use them.