á-amylase = alpha amylase, â-amylase = beta amylase ? tough to read those twiddles.
An interesting idea, you would have lower OG and lower FG, but about the same APV. Probably not much mouth feel or body either. As the article points out, converting the carbs to alcohol doesn't reduce calories.
Since extracts have been heat processed, there aren't any enzymes to work with. Also, there isn't any starch stuck in the mash to leave behind. If you are trying to cut total calories, make low gravity milds, ambers and browns.
Imperial (anything) = Super size