Well I was doing some looking around and could not find any posts on setting up a Spectrum DX9 to get 1TX channel 6 flight Modes.
So this is what I came up with.
I started by setting a 2 position switch as Aux1. (Switch A)
Then made 3 mixes to Aux1 > Aux1 and switch D (one mix for each switch position of switch D)
So Switch A and Switch D are used.
Here is the setup of P-Mix 1:
Mix 3 when switch D is in position 2 this is for modes 3 and 4.
So switching works as follows.
Switch A in position 0 and D is switched for 0, 1, and 2.
This gives you Modes 1, 2, and 3.
Switch A is then moved to position 1 which then changes right to Mode 4, and switch D is moved 2, 1 and 0.
This gives you modes 4, 5, and 6.
Then move switch A back to position 0 and you are back to Mode 1.
The Rate % is what the difference is being added to the other switch. So the first rate is for the switch A in position 0 and the second is for switch A in position 1.
Set your rate % to (ideally) produce PWM pulse widths of 1165, 1295, 1425, 1555, 1685, and 1815 milliseconds.
You can see this live in Mission Planner as you change the % rate.
I have found that different RX types the % rate needs to change.
Have tested with Spectrum DSMX, Lemon DSMX PPM, Lemon DSMX regular and the % rate is different for each.
So when setting up be sure you have the correct values for each switch position.
Hope this might help someone else.