I'll buck the trend here, I guess: the PIMETA is not up to the capability of the Senn's. The Senn's take a prodigious amount of power production to really shine. They are best served by something with a powerful discrete output stage that slews lots of volts and is back by a powerful power supply. Something like the M3 or a DB-equipped Millett on a TREAD or STEPS is probably minimum. A Dyna-series or Amb's B22 would be even better.
I have the Millett's, an M3, and the PIMETA's. Grado's sound glorious with the PIMETA's, but there's no point in even connecting the Senn's after you've heard them through a powerful Millett/DB or better. The PIMETA will blow any CMoy away and run rings around even a PINT, but there's a power supply ceiling and output stage bias limit that it just can't overcome.
You've got a set of $300-$500 headphones, there. They will soak up that much amplifier investment and more and still come back saying, "Feed Me!" The nice thing is that you are rewarded more for it.