Mixing 2 swashplateS

Hi
I'm almost done building my synchropter!
Now I'm trying get all 6 servos working correctly without any flight controller....yet. (Any controller suggestion will be appreciated)

FYI this thing works similar to Chinook -having 2 swashplates, 1 for each rotor.
The problem is rudder control which is done by lowering one swash and raising the other.
I just can't find a way to mix that.
Assigning Cyclic1/2/3 to a VirtX and use VirtX as source doesn't work.
However using Cyclic1/2/3 assigned to regular channels as source worked but that wasted 3 full channels and frames.

DEVO 12S
V5.0.0

Maybe my question sounds too hard

The real question is:
I set Virt4 as Cyclic1 mixer type (Simple/Expo/Complex/cyclic1 etc)
and then use Virt4 as Src on Ch1. This doesn't work. Ch1 acts like there is no input.
Using Real channel instead of Virt does work but I will run out of channel this way.

Is this normal?
How to get around this problem?