Just picked up a set of Philips Fidelio X3's from that great ongoing Woot.com deal. Amazon shipped them out in 1 day for free too.
I plugged them into my favorite iFi Zen DAC V2 using the single ended cable, which by the way isn't much longer than the one that came with my HD600's and I was not at all disappointed with the X3 performance...these are an amazing sleeper HP; I have the X2's as well and like the X3 even more, comfort and sound.
I then ordered this
adapter so I could use the 2.5mm balanced cable with the 4.4mm balanced output of the
Zen.
The X3 soundstage is just fantastic especially with the Chesky Binaural+ albums IMO, a couple of recommendations:
Amber Rubarth - Sessions From The 17th Ward 2012 HDtracks Binaural+ 24-96
Alexis Cole - A Kiss In The Dark 2014 Chesky Binaural+ HDtracks 24-192
Nothing like new HP fever.