Mike, I've had a look at Axminster's website and as far as I can check, the SK114 is manufactured with the thread as part of the body. The Torx screws just hold the backing plate in place, not an actual thread backplate, as was done with their earlier chucks. What adds to the confusion is that they use the term 'Super precision' in the title of their older chucks, where you can still get some backplates, but your SK114 is termed an Evolution chuck but they still put 'super precision' on the plate at the back of the chuck.
A lot of people have considered this a backward step as you can't change the back part of the chuck when you need a different thread but Axminster consider this 'one piece' construction ensures a more accurate chuck.
Unfortunately none of this helps you achieve your main objective, and I agree with you that thread adapters introduce problems, namely run out accuracy and they take up a lot of bed length. I also think they put extra stress on the headstock bearings.
I would concur with John (BHT) and give Axminster a call as they must know exactly what options you've got.