Seriously though, if you don't think the HD600 has some graininess (along with every other dynamic headphone) just try them next to some Stax.
I noticed grain before I tried the Stax 407 and once I compared them side by side it was obvious that the grain i was hearing was indeed there. It was there in every dynamic headphone I have. The TH-600 I demoed seemed particularly grainy for such a high end 'phone. I'm not saying it didn't sound bloody great because it did. ;)
So it's a bit like comparing a TN panel to AMOLED?