Re: my previous comments on HE400i soundstage...
Visiting my wife's parents for a couple of days which gives me a lot of time to listen to music and fiddle with my audio set up. I was looking at the viper effects on my X5iii to see if I could coax more width from the headphones. Previously I had left only Field Surround on and of course was busy turning effects on and off to see the difference. Turned off everything and realised that the surround had been having a drastic effect on the presentation, really hugely changing the channel balance and not in a particularly good way.
Basically, it's like I'm starting with the 400i's all over again and I'm much less disappointed with the sound staging. Still not that "like you're actually there" effect which I'm chasing but so much better than before: wider, more involving, more engaging. I think I'm in excess of 50 hours on these so there may be a slight settling-in happening simultaneously.
Overall, I'm very happy with these headphones, clearly even more than before! I find them quite addictive. I think they're an absolute steal at the current price.