Ok, I see what you are saying...Yes, I believe you can use the FY-31AP with the DX6i. Is your FY-31AP programmable via a computer?
I would imagine that you simply program the FY-31AP and then go fly. There may be a switch, in the DX6i, that you can program to turn the AP on and off. Not real sure.
I couldn't find much info on that AP. My laptop is acting up again. My opinion...yes, you should be able to use the DX6i because the DX6i is just the control link. Once the DX6i and your receiver are on, and talking to each other, your AP should be the one to tell your receiver what to do.