Yeah i dont like downsizing either there are some stoves that work ok with a smaller liner but downsizing would limit your future options. I am glad to see there is someone else here that supports doing it right and breaking out the old tiles when applicable.With Cracks in the flue tiles like the pictures shown you could probably go through your insurance to pay for the project as they were most likely caused by a chimney fire. In response to the posts you should not downsize the chimney liner size from the size of the stove outlet. You would need to have a company remove the tile liner in order to get the properly sized liner down the chimney with the correct amount of insulation around it.