RBR50 Port Forwarding not working as expected

I figured out my own problem.  Ultimately, I went back and re-configured the network adapters for the VM.  While I got the dual adapter configuration recommendation from an article where someone was trying to do exactly what I was doing, it never sat well with me -- a VirtualBox Bridge network configuration is a bi-directional access to both your local network and to your public internet, so it didn't make sense to me that you needed to have both it and a NAT adapter as well (which is far more limited as to what it can see).  

I disabled the NAT adapter, and ran all of my networking through the solo-Bridge adapter. And magically, my Orbi port forwards started to successfully pass through to the VM, and could be accessed from the public internet.  

Done!  Thanks for anyone who tried to help.