Just got me a set of HD650's, running off an Audioquest Dragonfly streaming Spotify @ 320kbps. Not the pinnacle of audio setups, but the best I was able to afford. Gotta say, was a little disappointed at first -- they sounded exactly like my Shure SE535's.
Que a couple dozen hours of playback/burni-in, and I cannot take them off my head. They're really luscious, a lot more detailed than the 535's, not a trace of harshness/sibilence, comfortable (the clamp has eased up to a gentle squeeze) and just so very pleasant to listen to for hours on end. They really make me happy! I think the Dragonfly is a good pair-up -- it's oh-so-slightly bright, helping to bring out detail and sparkle, with plenty of power for the cans. I've never gone above the 70% volume mark on my laptop. A nice little setup, all for under six Benjamins.
Anyway, just wanted to say thanks to Head-Fi. The forum has been super helpful and very accurate with their description of these headphones.