I actually was using this on some Sony headphones I have had for about 8 years when I first got it. For 8 years I listened to these headphones and never thought twice about them. When I had the amp hooked up, I heard EVERYTHING I was missing, including alot of the sound. I replaced the Sony with the AKG K240 Studios Right before they started making them in China (luckily on my part, because the new ones suck). I LOOOOVE them. but when I try them without the amp there is still alot missing. They are closer to my Sonys. I guess the iPhone isnt the best way to play music anyways, but I feel I am becoming more and more attached to certain recordings. I have a much better appreciation for the artists that spend the time to really lay down some amazing tracks. its worth it to me. I just bought a Pair of the Westone UM series, the one with 2 drivers. I have yet to receive them, but I read a review about them from the same guy that convinced me to buy this amp. He has steered me into the AKG and this so far, so he is 2 for 2 in my book. Sonics tracking said I will have them on Monday so I will review them once I have had some time. But this amp is a great choice! Great music reproduction!