Can you explain in a little more detail how to see through which CF servers the traffic goes - and are there any settings that @AB de Royse777 can try to overcome the problem?
You should be able to see the alt-svc header in the get request for the initial load of Bitcointalk.org. This should be automatic and I'm not aware of any settings that can overwrite this. If you're consistently encountering that CAPTCHA challenge, then I'm inclined to think that it would be some other issues. Without knowing how exactly it is setup, I'm afraid I can't provide much inputs over here.
Clearing cache, refreshing circuit and changing the security level are things that I would recommend trying.