I have the 600s, the 700s, and 800s. They get plugged into a DNA Sonett on its low output impedance setting, which is 28 ohms. It's a natural progression of more clarity across the board as you go up the ladder. Soundstage gets wider, also. I should mention that I've Anax modded both the 700 and 800, and though I find the changes minor, they're audible and preferred. I go back and forth with the ear cup foams for the 600s. Removing them is almost like a partial step towards the 700s, but sometimes I like the little bit smoother sound with the foams in place. And that being said, going in the other direction, I gotta say the 600s are great. They do it all quite well. The 700s bridge the gap nicely, they can be smooth but also do that almost clinical thing the 800s can do. A good blend between audiophile and music lover.