Hello tmbm50, you might try ducting the other way... what I mean is ducting return air to the current fan on the LL stove.
At Lowes and HDepot there are ductwork flanges as well as plastic flanges that can be screwed to the inlet of the didtrbution fan on the stove..
Then hook a 4" or 6" cold air return duct to the fan. Pull the air from the farthest point in your house that you can.
The reason that this works is that when you start adding ducting to a stove, you are trying to make it act like a furnace. A furnace never pulls cold air from a basement, it has cold air return ducts that hook to a fan box on the furnace. With the forced hot air going out, and the cool return air getting reheated, it creates a circulation loop.
When we add a hot air duct to a stove, and try to push the hot air into upper floors, we are neglecting the other half of the circulation loop.
You can use inexpensive dryer vent fo this cold air return, unless you route it through unheated rooms.
Hope this helps. Greg L