Pixelshades luma keying

I need to mix two (or more) video, both with white background.
Using the RGBlumaswitch downloaded from catweasel (“RGB video.fx” from http://vvvv.org/userpage-18 ) I’m able to remove the background from each video (inverse luma keying)

Now I don’t understand how to mix the the two outputs. I mean from the “RGB video” node I have already a EX9layer, it’s possible to merge two EX9layer or I have to do everything inside the pixelshaders node? I’m starting now with the HLSL and it’s little bit hard for me :)

feed your RGB shaders into a “group” node

yeeeeeeeeeeeeeeeeeeeeeee thanks!