Only 25 hours on the TH900 and they're already changing for the better. Great cans, and spectacularly good for closed ones. I take back the low-volume listening comment...they're good at high volumes too. They play in the same league as the 800 and HE6 (though the 800s are still my favourite).
As for the HD800 cables, people need to realize not all cables are created equal. The previous DHC flagship solid core cryo UPOCC silver was easily trumped by the new rectangular silver flagship that DHC replaced them with. Smoother, more natural, bigger soundstage and slightly better bass weight.
Moon Audio's Silver Dragon V3 is pretty good, but not quite at RS' level. Watch out for low quality silver from others who sell for cheap...it can make the sound dry and harsh.
Also, just to clarify, with some of my setups, copper does sound more pleasing. That's why I keep both.