I have done a great deal of testing with many opamps on many different soundcards including discretes.  I also build custom units for my testing so if you have any questions that I may be able to answer please feel free to ask.

Any of the cards with replacable opamps offer you "tunability" That other cards do not have.  You can use your favorite opamps that improve the sound quality or change it more to your liking or making the card a better match with your phones/speakers.