A short while back I was displeased with my MKIV SE and was looking to sell it. Fortunately for me, I had no takers, and closed the classified and decided to burn it in for 200 hours. I'm not sure if it was the burn-in, or the act of actually playing with the various gain settings, but the sibilance I was originally unhappy with (with my 600 ohm T1) is gone. I've also discovered (duhhhh) that ALL my phones sound great at one or another gain setting (Mad Dogs, HD-600, HE-500). At the original default gain of 3 the lower impedance phones were lacking in bass. No longer.
Now that I've decided to keep her, I'm going to try rolling some driver tubes. They are a b*tch to remove ---- I assume the solution for you tube rollers is the same as the one I'm using for my Lyr ---- socket savers to elevate the tubes for easier removal?