I'm about to pick up a pair of ATH-M50s headphones and I'm wondering how much of a difference a DAC will make. I'm thinking about the Fiio E07K. I'd use it with both iPhone and computer. Can you really notice a big difference in the sound quality?
Only you can truly answer the question of whether or not a DAC will improve the quality. Lots of people will probably never be able to tell a difference if they did a blind test.
Personally, I wouldn't bother. The M50s are good headphones and will sound great as is.
My theory with this kind of stuff is if you have to do an A-B comparison, back and forth, to notice the difference, it's not worth it.