I feel bad looking at Larry's post as I realize I have been dumping on Apure. Hey, if you like silver then silver it is, that is why I keep telling everyone "Cables Make a Difference" and just because you cant hear it doesn't mean I cant. Judge with your ears and try to build a system that full of components that complement each other in a way that is best for you. Use your ears and ditch all the graphs and such. I chose as well as I could by reading constantly and then the other half of the equation was tuning and now I love my rig man!!!
At present the only reason for me to try other gear is to get a wide variety of experiences, not subtle ones like cables typically are stated to give. A minor side reason is physical comfort. While the HD600 are indeed very comfortable and I can wear them for hours, I would prefer eventually having a phone that sounds as good or better that has larger openings on the pads because currently my ears touch the edges of the pads and while it doesn't hurt it is distracting. I hear the new HD800 solve this as well as other phones. Really the only phones I've even considered buying at this point first had to pass the 'close to HD600' test then the next criteria was 'are they more comfortable'. I will never own a supra aural main headphone, but maybe could have one for a different sound flavor every once in a while. I tried the Audio Technica ATH-70 electrolets at the Dallas meet and was surprised with the comfort from the supra aural phones, and at the same time they were Stax like in signature and close enough to HD600 to be interesting. Too bad they are so rare. They are cheap too.