and don't forget driver variation. I'm certain with the senn100's there is huge variation from one set to another and likely one driver from another...hence the DIY benefit but don't lose sight of this fact like 99% of headfi who hasn't even dis-covered the fact of driver (headphone) variation from one set to another.
I have gotten 3 different PX-100ii drivers and they all sound slightly different, one is on the bright side, one is fairly neutral and one seems to have limited dynamic range. All tested in the same housing, ear pads and wires.
There's more than a slight difference in the three pairs I have.
I also find the closer the driver is to the ear the better SQ.