Any idea how a an apple brandy stout would work?

I would try it! If at the end the soup is a bit too sweet for you just stir in a splash of red or white wine vinegar to balance it

I think the apple brandy stout would be a wonderful selection for the alcohol in the original (red wine or stout)...it will introduce a little more sweetness than the original had, but not a lot. And the combination of brandy and beer will give added depth of flavor.