Thanks Lydiot, appreciated.
I perceived Nuendo’s “group” to be something other than a send buss, more as a subgroup (output routing rather than send)? I will take a look at that again to get my head around Nuendo groups a little more.
You got it.
Nice thought - that would get around some other restrictions imposed by Nuendo (i.e. there is no way to design your own children sets like PT and DP (& reaper etc) do with their simple matrix setups). This solution you propose however does largely replicate what already exists in that Nuendo lets you choose to send a subset whereas the problem is how to receive a subset.
Interesting, but does not produce the signal flow that the problem context provides. In this scenario a stereo send would suffice I think.
No apologies needed - Appreciated. 
I get the feeling that the difference in design might be this - busses in DAWs are usually treated as their own entity - then you connect objects to them at either end. Nuendo does not seem to do this but treats the busses almost as if they are in an integrated circuit. I could be wrong, and hope I am. There is lots to like about Nuendo (and I am really sick of being bent over a hard surface by Avid so am looking to shift my software and about $250,000 worth of Avid hardware out the door if I can and replace with something else) but if there is no way to select a child buss as an input for an FX or Audio channel then . . . . . . . . . . NFI.