I agree with chesebert about HD650 (and HD600) dynamics, not that they are bad, they are just not outstanding for me. I have had and sold both, preferring my Monolith M1570 to them (both for dynamics and timbre). When you play a piano, even a digital one, you are creating and controlling yourself in real time the sound and the dynamics, not simply listening at a recorded performance: You may not know what the intended dynamics are on a recording, while you know very well how your own digital piano should (and could) sound on headphones and the dynamics it should express, expecially if you have a good reference speaker system in a good treated room (and I have both).
It may well be that transients are on some headphone somehow overstated compared to your reference speaker system, this happen to me with my ETA Mini C, to the point that it could sound sligthly unnatural (but... sligthly): In this case I could prefer something less aggressive. HD650 is just a preference, for some piano players it could be dynamic enough, in my opinion you can find better as to dynamics, nowadays.
Just to say, I prefer KPH40 to Mini C and M1570 just for piano playing. Pianoteq 8 is particulary good in expressing the full dynamic range, probably the best thing besides a real piano, so it's a good test bench.
what he said. Piano player here. Hd650 or Onkyo A800 for piano. But edge goes to hd650 for more attack and warmness in mids
