I bought the first pair of Sennheisers because I wanted something above supermarket-quality headphones. I bought a second pair so that I’d have one at home and the other at school.
The problem with the Momentums is that they have a somewhat uncomfortable headband and they have a proprietary connection for an iPod. Yes, you can connect the headphones to anything with a standard 3.5mm jack, but the controls should also work with everything.
The problem here is that the control affects the device, not the headphones, which is actually rather odd. I’m sure there was a good reason. Perhaps the intention was to obviate confusion about where the volume should be controlled from so that a control which affected the device removed a link in the chain. In truth, even when I have the Momentums connected to my iPod (usually through the Dragonfly or FiiO K1), I control the volume from the device because the control is so far up the cable that I’m not aware of it and have no idea which button raises the volume or lowers it.
With the FiiO E17K or the PHA-1A, volume is controlled from the DAC, although the former is awkward to use easily, and the latter has a pitiful battery life.
Out in Coastal City, which is yet another of those ubiquitous Chinese shopping malls with the usual shops (you could play a predictable game of bingo with them), I had the chance to try a range of headphones, including a pair of Bang and Olufsens. I was trying music off my iPod Touch through the Dragonfly. Conclusion: the Momentums were more than adequate.
A comparison between the Momentums and the HD 599s is interesting. I was listening to Landscape through the Momentums through the ifi nano. The music seemed much more base to me than it had previously, which I attributed to the nano, but when I tried the 599s, the base was far less prominent, and the sound had a much airier quality to it. In addition to this, the volume through the Momentums was louder (as it was through the Marshals).