I have both the DT 1990 (I use A-pads) and Edition XS.
I’ve only had the XS for a day but these are my initial thoughts:
The biggest difference I’m noticing is that the XS sounds way more open than the 1990. It lets a lot more sound in and out.
The 1990 has substantially more bass, but the XS’s bass is faster and more responsive (seems like planars at work here). I miss the rumble from the 1990s but ultimately I prefer the XS here because of how clear the bass sounds.
The mids feel a little recessed on the XS but once I EQ’d them up a little they sounded fine.
The treble on the XS is quite strong. I’m happy with it, but I personally like the 1990’s treble a bit more.
In terms of comfort I prefer the XS because of the ovular earcup shape, though I wish it had a little bit more clamping force like the 1990.
I’d have to say the XS is an upgrade over the 1990 for its spacious sound and that planar bass.