Not sure about arc

EPA= End point adjustment. This adjusts the amount of range (left Right) you give your servo

Sub Trim= Pretty much the same as trim on your other old radios. It just adjust the center point of the servo.

Dual rate i believe adjusts the throw? maybe someone else can help.

Personally once you set these to where you like them, I never touch them. The one i play with the most is the sub trim and and the epa for the different track configurations