In the 9c to set the gy 401 gyro you don't use gyro sens mixing. that must be inh. U use instead the end point adjustment. You set the sensibility of the gyro as a normal servo rate (channel 5). Channel five is related to a 2position switch so when It's up you set the avcs mode when you flip it down you set the normal mode.
Then you turn on the radio in avcs and after you just flip the switch.
If you would like the switch to operate in the poosite direction (IE avcs down, normal up) you just reverse channel 5 like it is a servo