I felt compelled to write about the performance of the HD 650 when used with upgraded cables. I purchased my HD 650s used from a Head-fier in Canada. They came with a nice burned-in Stefan Audio Arts (SAA) Equinox cable which I compared with the stock cable, and there was a very big improvement in performance. After using the Equinox cable for a long period, I recently upgraded to a  used SAA Endorphin cable which added increased performance I did not believe possible, especially in the area of bass authority, timbre naturalness, and soundstage renderings.
 
I also have tried and use the Cardas cable on my HD 600s which also adds noticeable improvements, although not as great as those generated by the SAA cables on the HD 650s.
 
I listen to vinyl on a VPI Aries with a Clearaudio MC, Nordost Tyr cables to a  phono stage in my Spectral preamp, then out to a WOO WA6 SE fed with Nordost Freys. I also use upgraded power cords and power conditioners as well as BDR carbon fiber isolation devices.
 
After listening to a bunch of cans at last weeks' CanJam at the RMAF in Denver, I am still impressed with the HD 650s and their performance vs price. I did listen to the new HD700s but not long enough to form a strong opinion, but they sounded better to me than the HD800s. THE AUDEZE LCD-2S WERE AMAZING with ALO cables into a Ray Samuels Dark Star!
 
In conclusion, if you really want to get the most out of the HD 650s (or the HD 600s), try some of the aftermarket cables available, if you can, on a demo basis.