The improvement is in your mind. Be more specific about the test procedure and results. 5 vs 5.1 don't mean squat.
The opinions are widely scattered when it comes to the "shrink" program with the best picture. This tells me that the differences are so small that they cannot be reliably indentified under normal viewing conditions.
The most critical factor in picture quality is the percent of video compression. A shrink program that will allow you to remove the most amount of unwanted materials will yield the highest "quality" picture.