I think you’re going to struggle with the AR8000 receiver. You need a receiver with a serial/S-bus output. If you want to stick to the DX7 then you need to look at the serial receivers. You may be able to re-purpose the satellite receiver that you may have with the AR8000, but that could be a pain in the butt. I think things like the SPM4650 or 51 will work but you won’t be getting a ton of range with them.
If you’re entertaining the idea of Crossfire, then you might want to go that way. Or ExpressLRS. Those systems are more suited to flight controllers such as what you would use with ArduPilot.