Hmmm, didn't seem difficult at all to drive when I heard it at the TO meet. Not sure if Ray has the bass light or bass heavy version though.
Then again, I was listening on the B52, the apache and my amp, so I don't *really* have any clue how hard they are to drive... The B52 and apache may not be stellar designs, but they put out a fair amount of voltage swing and current AFAIK. I guess I was just under the impression that they weren't that hard to drive...
As for them being the hardest headphone to drive... I take it you don't have much experience with the K340 or K1000?