I made an account to be able to reply, as I've been comparing them last week extensively (among other headphones). I used default pads/filters (noticed them when I was about to leave so couldn't play with them). While the Stealth is outside my budget, the Noir luckily is within reach. I say luckily because I really like the headphone. So what about the differences. To my ears, the Stealth is very transparant/neutral/analytical with an impressive open soundstage. I've not experienced a close headphone before to have this open airy sound. But, it's also a bit sterile or dry at the same time, which is perhaps perfect when you use it for mixing/mastering tasks, but for music listening it's sometimes a bit boring. (Now it sounds like I don't like to listen to music with the Stealth, I really do though!)
The Noir sounds really good to my ears. It seems to have a more exciting tuning, with a very impressive low end, like a very good integrated subwoofer in a stereo set, but never too much or fake. The mids sound smooth and articulate at the same time and the highs are crystal clear. I really couldn't find a quality in them that I didn't like. Everything about the Noir sounds fantastic to my ears. Soundstage is wide and big and pretty airy, especially for a closed back. Not as expansive as the Stealth, but I don't mind that to be honest.
For studio work with mixing/mastering tasks in mind I would pick the Stealth (if I had the budget), but for pleasure and simply enjoying music, I prefer the Noir. And I'm not saying this because I want to like the more affordable headphone, I'm unbiased, I have no issue at all liking something better even when it's unobtainable for me.
I've tested these headphones on a desktop headphone dac/amp but I forget the brand. It was a $1000 something unit. Not ultra fantastic but not bad at all I imagine.