Because I didn’t mention it before, I think the original problem was that the Steinberg and Voxengo plugins were only seeing channel 1 and 2 when first inserted in the Montage Output of the 4 channel montage, which is definitely wrong and should be fixed in Wavelab.
If you don’t need or want channel naming in this case, I wonder if the 8 channel standalone configurations route as expected. I didn’t try that.