Any way to assign to 4 input channels on a VST effect?

Right now I use Plogue Bidule to do this, and I can get it to work, but I tried and failed to do it in Sonar alone, probably because I'm doing something wrong.

Here is what I want to do:

I have made a Reaktor ensemble that takes two stereo inputs (4 channels), does some slicing and dicing processing on them, and then outputs a standard stereo signal.

When I load Reaktor as a VST, it only shows two channels to Sonar. If I try to use the Reaktor Surround VST effect (with 6 channels) I can't seem to find a way to assign to the individual Surround channels in the effect.

I load one VST for the source of one input and a different VST for the second stereo source.

I just can't seem to find a way to assign the two stereo channels to the audio track Reaktor is loaded as an FX.

Inside Reaktor, when I hover over the 4 inputs I see these info popups:

Plugin Bus 1 Input 1
Plugin Bus 1 Input 2
Plugin Bus 2 Input 1
Plugin Bus 2 Input 2

In the Sonar track assignments for the two synths, I see Reaktor Surround Input 2 and Input 3 available, so I send to each of these.

I don't see any signal inside Reaktor.

Any help or ideas would be appreciated. I've tried various kinds of sends and surround busses, and I've looked over the help files for this sort of thing. I see the surround panner and stuff like that when I use surround busses, but I can't get at the individual inputs.


EDIT: here is what it looks like in Plogue: