I purchased the MHP1000s at House of Music SF on the 8th November 2014. BTW, while I was there, met CEO Charlie Randall and had him sign my McIntosh book.
Initially, I had no intention to purchase the MHP100 headphones. In fact, I was dead set to buy the Grado GS-100e.
I listened to both headphone options on my Astell & Kern AK240 and the McIntosh MXA70. I was surprised how well MHP100 sounded over the Grado GS-100e at its low, mid and high volumes. The MHP100 refused to distort. Contrast, the Grado GS-100e distorted shortly after a mid volume push. I also thought the Grado sounded overly bright and the base a bit artificial.
What stood out was that the MHP100 produced shockingly crisp clear vocals. Some of the vocals I tested I could hear the breath just slightly before the vocal kicked in. The Grado muddied the vocals and they sounded a bit distant. The MHP100 seemed to bring the vocals forward as if the artist was right in front of me - front and center.
Just an opinion and not based on any fact, I believe that McIntosh was very OCD about the performance. They are amazing. I say this because I expected them to be lack lustre.
The other thing I noticed is that sonically the MHP100 reminded me of my Martin Logan Summit X speakers. So that was awesome for me.
I was surprised how disappointed I was with the Grado headphones when after reading glowing review one after another that they stood up to the MHP100 so poorly.
BTW: Ron C stated that yes, the Grado is 32 ohm and the McIntosh is 250 ohm. This is intensional because these headphones will function with ALL McIntosh equipment every produced. They will play on a portable device but will be power hungry and quickly drain a device battery.
Something I noticed is that the MHP100, for me, performs poorly using an AudioQuest Dragon Fly DAC. It does, however, perform decently with the Astell & Kern AK240 and of course, on all my McIntosh equipment.