I have been today in an Audiophile listening salon, and had opportunity to head HD600, HD650, HD598, and I think the last one was the HD558. I listened to some very dynamic classical track with some quieter parts, and then loud trombones, timpani etc. All these headphones sounded amazing for their price. The obvious winner for me as well as for the salesman was HD600. Very warm, and highly detailed sound. I never heard so much detail in my life, even in philharmonic hall. The HD650 were also very detailed, not less than HD600 I would say, but the bass wasn't there. Obviously there was strong bass, but on HD600 it was stronger and more natural. I say natural, because (as mentioned few posts before) natural for me is the way things sound in life. So when I hear timpani, I expect it to make an impact, and HD600's do timpani like a real one. They actually do every single instrument like real. Also the 3D placement of instruments on HD600 was wonderful. I think I perceived more space on HD600 than on HD650, because of that more bass. In real life bass gets amplified by philharmonic hall, so this is what I would say I have heard on HD600, a magnificent hall, and every single instrument was very precisely placed in that hall. What really stunned me was exactly that, and this is what is missing on Momentum's. However this is also what is missing on HD598, and HD558's.
If I were to compare these four headphones to Momentum's, then I would say Momentums are like HD600. My next buy will definitely by HD600, and because I know how these three other sound, I would never buy them, because Momentum's are better for me. I would also not buy HD650's, because they are cooler than Momentums, which is not nice I recon.
So yea, Momentum's do sound like HD600's, but the later ones do may more detail, and more space, and more precise positioning. Honestly, the placement of sounds on Momentum's is really poor, but I don't really complain. Their purpose is to be portable HD600's, so they are as good as it is possible for portables, but HD600's are many times better, like 150 euros better
I have bought some tracks on HDTracks: Jurassic Park @ 24bit/192kHz, and Daft Punk @ 24bit/88kHz. I'm playing that on Linux though Jack. I fixed the sample rate to 192kHz (Intel HD audio does not support 88), so Daft Punk plays in upsampled from 88 to 192kHz. The sound quality is amazing. Many times better than CD. And I am listening on Momentum's directly from my Laptop, and it copes very very well with 192kHz data. Clear sound, very well defined bass, clean mids, nice treble, generally going from CD to HD does make a difference on Momentum's. I can only imagine in some very close future my appreciation in HD600's thread. Still wonder how LCD's sound though...