Listening to the Momentum and Amperior right now...
Starting out with build. I feel as though the Momentum wins hands down. To me, the Amperior feels like a fairly cheap headphone. Save for the aluminum ear cups, the rest is plastic. The most suspect pieces are the plastic slides that are used to adjust the ear cups. I am just not confident that these would hold up well over time. The Momentum obviously uses a metal headband and overall just feels like a more solid package. The leather on the headband looks well stitched and the logo's appear to be laser etched on small metal badges vs. the poorly painted on logo's that the Amperior has. This is really no comparison. Anyone that sees both of these headphones will find that the build and feel of these headphones are on opposite sides of the spectrum.
Comfort. I found the Amperior very comfortable. The felt-like ear pads stay fairly cool during long listening sessions and the headphones are fairly easy to position correctly. A few criticisms though are the clamping force feels a little tight and the adjustment sliders don't like to hold their position while you make minor adjustments. The Momentum is really just as comfortable, but in a different way. The leather touch-points on the ear pads and the inside of the headband are very soft and feel good to the touch. Since this is a circumaural, there is little to no pressure on the ear. Ear cup size, as discussed, is a little on the small side. Luckily, this was not an issue as my ears fit perfectly inside the headphones. Clamping force is less than the Amperior, but still very firm. Neither headphone is going anywhere while you move around. A criticism of the Momentum would be that while the leather appears to be great quality, it is still leather, and does get a little warm over long listening sessions. I would give this to the Momentum, though it is fairly close. Most that like one, may not like the other though. Again, they are very different in the way they fit.
Sound. This one was a little harder to judge. Again, very different headphones. The Amperior does have a more neutral sound signature for starters, with the punch up in bass on the Momentum quite obvious. It wasn't so much that it ruined the sound for me though. It was dependent on the genre. For classic rock, like Skynyrd, I felt it took away from the overall sound, clouding the vocals a little bit. The bass was deeper, but much less precise than the Amperior. That said, it was still more precise than other lesser forms of cans. On O.A.R. though, I kind of liked the Momentum version. The vocals were high enough frequency to escape the low end fiddling by Sennheiser, which allowed both to jump out on the track. Both headphones were incredibly detailed, though the Amperior being less affected by enhanced bass seemed to come across a little more articulate. I would fault the Amperior for being a little shrill, though this is less apparent when not A/B'ing the two. I would have to give the edge, overall, to the Amperior. I will say though that I tend to prefer neutral headphones. If you like a little additional bass though, the Momentum is a STRONG contender. I would really like to hear a version with less bass, and maybe a machined aluminum ear cup! Combined, they would really be the best of both worlds. The fit, finish and style of the Momentum, with the sound of the Amperior! I can dream, can't I?
For reference, I listened to both headphones via my Pioneer Elite SX-A9MK2-K 2ch integrated amp. I listened to various tracks/genres encoded in ALAC out to the Burr-Brown USB DAC on the aforementioned amp.
Great comparison. Now I am curious for Momentum vs. Yamaha Pro 500 as it has aluminum cups.