Agreed, M50 was an intimate engaging experience and definitely not distant sounding, anything more "forward" and it would be impossible to process any decent soundstage. Actually I like this kind of presentation but optimally with a bit more expansive soundstage than M50 at least, Denon HP700 does excellent job with this with a forward/engaging/intimate presentation but with a reasonable expanded soundstage for a closed headphone. But yea I hate "distant" or laid-back sounding headphones (but I don't like bright headphones either, I don't mind forward midrange but don't like emphasized highs) as I want to be immersed with the music which to me personally is coming from a both a bit boosted bass range for increase of immersion with the "thumps" as well as a forward midrange for that intimate "feels like the singer stands next to you"-presentation.
How would you compare M50 vs S400 in highs? My interpretion of M50 is on the border of becoming bright headphone, it can have some sibilance due to a spike there somewhere around 8~10kHz range but otherwise it's on a fairly neutral level, I personally would optimally want a more even highs range compared to M50, the Q40 have very nice highs for me, like M50 but without the spike so overall Q40 feels very neutral in the highs, just hasn't got the best extension and rolls off at like ~15kHz so it lacks some of that "airiness" of open or highend headphones but to me that's not such an important aspect.
