The PB2 is said to pair well with the mad dogs and it did when I was driving it via using the iphone4s as a DAP. I bought the DX50 as an upgrade DAP and use the PB2 to amp the output but after listening to the mad dogs from the DX50 alone its reaches 90% of the SQ and loudness levels of the PB2, IMO. So no real need for my PB2s now. I still might keep the PB2s because I have the HD600s coming in the mail and the DX50 may be insuffient to drive the high impedance cans
Just a few more day until they arrive hey? You're in for a treat!