IME a high quality food and big frequent water changes will keep them thriving. I usually do 50-80% weekly water changes and feed New Life Spectrum Thera+A exclusively. The discus at the shop were breeding in front of customers on NLS alone.
The issue with discus is that they are not as hardy and therefore not forgiving. When you miss water changes you will see it in them much easier than you would ever see it in almost any other fish.
One thing to keep in mind though is where your discus come from will dictate the minimum level of care they need. For example, a discus that went from a large farm, to a wholesaler, to a LFS, and lived through all that and looks good in the LFS is going to be hardier than one you mail order from the nation's top discus breeder. If the breeder does 90% water changes every other day and you only do 50% every week his discus will probably not do nearly as well as your others, it may even die. If you pick the right ones from the LFS you can get very hardy, beautiful fish that are hardier and cheaper than high end ones. You may want to check out my article on why pure breeds are not ideal, it goes into some more detail on this kind of stuff.