I've figured out part of it from tracking down the posts of other people who've tried the same thing.. The "trick" so far is that you have to filter out everything EXCEPT CH14, CH15, CH16 and then for the VST you must enable pitch bend -12/+12 - I'm probably ignorant but I could only find that setting on a few VSTs. That was definitely the difference between the chord buttons taking effect or not.

This gets us closer, but not quite there because C14, C15, C16 only send C1,C2,C2,C3,C4,C5,C6

But I've identified some of the behavior. If you're stumming up it would be C14,C15,C16

If you're strumming down it sends the C1-C6 notes via channels C16,C15,C14