Hi itman,
Don't have the other two headphones you mentioned but have done demos enough to know while good for classical & this is highly subjective & personal, those headphones aren't for me.
The PM3 has no problem with classical or any genre for that matter, just depends on your taste.
Keep in mind, if you want to be technical, which is why it's tricky to compare, Momentum 1 & 701 have dynamic drivers, wheres PM3 are planar magnetic, hence the name.
Main difference being one has a driver which moves as well as vibrates more than the other, think a small speaker driver vs a flat sheet which has less physical movement caused by an electric current &/or signal going through it.
In most cases, Dynamic driver (the small speakers) generally not only need more signal to move &/or vibrate but also takes a bit more to stop.
Whereas, a Planar Magnetic Driver can move & stop with more speed and precision.
This is also where tuning and impedence rating comes in as the latter is defined by how little electric resistance it needs to be efficient. (lower is generally better)
Imagine controlling waterflow through a tap, the more you turn, obviously the more water comes through. This is where volume & audio level comes in by turning the volume knob on your gear to where you can hear comfortably and clearly the details from your source (music, speech, etc) not how necessarily how loud it is.
This is subjective but impedence can be seen as how little you need that tap or knob to turn to enjoy it.
A good way to test equipment & gear to see how good it is, by seeing how low the you can consistently make it to enjoy it without being too loud.
If something is just loud, doesn't mean the detail is always good &/or clear either but that's another topic.
Hope this helps.
