Thanks for the details explanation, makes it way easier to help @HighTech , fantastic job!
Now, here is my "reckoning" for the lack of a better term lol
So, logically, Im fairly sure you can do this, but you need to make sure link selection is configured properly. So, in your case, since CP has only 1 link, tunnels would always "terminate" on same external IP. Now, technically, since Sonicwall has 2 ISP links, you really would need to have 2 separate VPN tunnels. In that case, Im thinking link selection could look something like below...
Let me know if that makes sense. If not, we can do remote and go through it, if you are allowed to.
Andy