That link you gave is really helpful. I don't think I'd seen your reply when researching.Finally, I move heat from the basement through the stairs just like you. I do it like this.
The cat and I have been working on my husband to let us do something similar to your fan/vent for the last year, but he's not willing to cut holes in anything yet. Hence the resorting to trying for a second stove which would be a lot more $$ and silly. We've definitely been working on upgrading insulation and next on the list is windows.
We'll keep trying.