Yeah, the 6SE, paired with an amp that mates well with it is an endgame headphone. It can be a bit tricky getting a great pairing with them as they lean a little bright to me stock, so I don't quite enjoy them as much on brighter amps. But get the pairing right and you're going to struggle to find an upgrade anywhere near that price, IMO. They kind of just do everything, really well.
That's great you found a closed endgame. Closed gets harder, for sure. The sound changes a lot when you close the cup - especially the sound staging and openness.
Ultrasone does an incredible job with closed backs though - I'm not surprised you found it with an Ultrasone. Ultrasone titanium plated drivers are fast, detailed, crisp and they do a wonderful job. I wonder how you'd like the Natural - to me it's like the best monitor sound, picks up so much small detail and stays so tight and controlled with some great punch. It is like the culmination of everything I've loved about Ultrasone, crisp, tight, punchy - but it does it the best of all their models to my ears.
It's a headphone I feel that would be incredibly good as a tool for like an audio producer due to the way it clearly and tightly shows you everything in a track. Bass is so tight and defined. It's really just like the best monitoring sound I've heard, not sure how to really put it better than that.