Here is how I would set that up. If you are using only satellite Rx, and not a standard Rx, they yes, your channel will be Aux2. However, if you are using a standard Rx with the 3GX, then you need to set the gyro channel to Gear. Set the switch to the gyro switch (unless you want it on F-Mode, which I suggest against until you start flying pretty hard core 3D and need the absolute max tail hold) and set the numbers as follows
Position 0: 45%
Position 1: 0%
Position 2: -100%
The reason for this is you will always fly in position 0, or the switch all the way up. This will put your helicopter into HH mode and it will be the most stable. Position 1 is to test the tail if you ever need to without input from the gyro. You can set this to another positive value, such as 40% just in case you think 45% is going to be too high. Position 2 is going ot be used right before each flight. It is used to center the tail blades on the helicopter. When you move the heli, the tail blades are going to move, and because it's in HH mode, it's going to hold that position. So right before you spool up, flip the switch down into 2, then back into 0. This will center yoru blades.
Doing it this way will get rid of the Hold setting. You never want to use a negative value when you are in the air. If your tail is not 100% accurately and correctly set up, the tail can and will drift off, quite quickly in most cases, causing a loss in orientation and ultimately a crash.
Hope this helps and didn't sound too confusing.
