I have actually not made those videos because I have already covered it in other videos. You are correct, I use the DX9 and on my birds with a BX gyro, I set them up as follows. No mixing, use 1 servo 90º swash, or normal, depending on the Tx being used. Go into the flight mode (after setting up helicopter model type, name and so on) and turn the hold switch on. From there, enter into the main menu and turn the tx on.
In here, first thing you will do is follow the steps in the video to program it. With a new model, you have everything linear which is where you want it when setting up. Once you complete all setup, go into the Tx and set your DR/Expo. I know, it says to do it on the gyro, but I still do it in my Tx. Just make sure you don't limit it too much where you can control it. For me, on a 3 position switch, I set it at 70/+35, 86/+35, 100/+35. This is just my DR/Expo settings, change them to fit your flying style.
Then I set the pitch curve. I only mess with Normal and I change that to 46-48-50-75-100, the other 3 are left at linear.
Throttle curve, I set normal (with a good ESC mind you) to 0-75-75-75-75, idle-1 to 87-87-87-87-87 and idle-2 to 100-100-100-100-100
Gyro on the DX9 on a 3 position switch I set to +45/0/-45 for high, middle, and low on the switch. This allows me heading hold, no gain and rate mode. no gain and rate will allow me to center my tail blades before taking off.
And that is about all I do. DR/Expo and tail gain controlled by the Tx, the rest by the gyro. Hope this helps.