Cant help you much with the DX6. I think it has throttle curve points, but I am not sure.
Trex 450 - Yes, you will need to move throttle from time to time to maintain stable hover. Especially outside with wind which can cause transitional lift.
Setup for 450- go here: http://www.helifreak.com/showthread.php?t=11373
As for the AXE CP, without the motor attached, check to see what your blades do when you move the throttle. If they stay the same then you have a setup error in your radio.