Well, you have my thoughts on M-100. I owned Momentum for a day. While some would say that's not enough time to evaluate, I knew fairly quickly they weren't for me sonically ( although great looking, well built, light and extremely comfortable). The highs seem artificial and harsh. Overall detail in mids and highs inferior to M-100. Bass is loose compared to M-100, doesn't go deep enough and goes to high into the mids to the point that I felt there was some bleed.
There´s a lot of criticism about the momentum... you are not the only one in this forum to return them... That´s kinda sad, I really like the momentum appearance . Well that means the M-100 is my next headphone. BTW, I ordered the UE6000 yesterday! yeahhh!!