Not to knock on these, but for my preferences, the NOIRE X's were far more engaging and sounded right. The treble dip on the XO's from 9 to 12 KHz makes it a bit too warm for my tastes. As a treble head, I can do with the slight bass reluctance vis-a-vis. However, XO's treble is a bit too little in that region and below neutral for my preferences. I just got the XO's from Crutchfield and it was an instant return.
@Dan Clark made the NOIRE X's just too good for their own good.

That said, I could see people of the Sennheiser persuasion liking these for the warmth factor. The NOIRE X to me is the best middle ground of all headphones I have ever heard. Not treble happy, ear drills like a Beyerdynamic. Not overly warm like a Sennheiser. Not hindered by weird resonances like a Grado or AKG. Not sporting an upper midrange suppression like some planars like HiFiMAN. Honestly, the NOIRE X is the MVP of this headphone generation. It does so many things right and it is sealed. Basically, like the Ascend Acoustics SIERRA-LX pair I had. To be clear, the XO's are definitely not bad and whip the pants off of most if not all Sennheisers, all AKGs and Beyerdynamics, etc. They are missing something in the treble regions to sound right and not veiled (comparatively speaking, that is; these are
not muted!).