After much help from the forums, I've decided to get the DT990's Pro version. From what I've read, the differences do not justify the increased price of the Premium version.They are priced at $149.00 so that gives me some money to look at upgrading my AMP & DAC. I currently listen to my Custom One Pros with my FIIO E17. I am hoping to take my listening environment to the next level. I listen to my music from my Macbook Pro primarily and occasionally my iPhone. My budget is around $500. What AMP & DAC combinations would people recommend? I've seen some good comments about the Schiit Vali and the O2+ODAC COMBO.