I think a chart like that would be great too. it sure could help break it down for the end-user. as long as it was comprehensive covering ALL price ranges and that it was detailed with fact, not opinion. an excellent idea!!
The only issue with creating a sound card "heirarchy chart" is the fact that everyone has a preference. What may sound great to 1 person, may not to someone else. Features that are important to 1, such as EAX....may not be a factor to someone else. In any case, the "chart" will be almost exclusively based on the "reviewer's" preferences.