In order of purchase hfi15g, Zino, hfi2200 v.2, hs15, PRO2900.
I originally bought the 15g to see what the ultrasone sound was like then fell madly in love with it. The 15g is also my go to portable. The Zino was bought at a deep discount. 2200 was purchased used and became my favorite multipurpose headphone. The hs15 was bought for console gaming. The 2900 was purchased yesterday and this is the 3rd time I've fell madly in love with ultrasone.
As far as source and amplification, I currently use an m-stage class A bias mod with dual OPA0627's connected to my pc, 8gb zune, and an hp touchpad.