I only kept the SE846 for 5 days, and my memory of them is now a bit hazy. I was able to pick out some sounds in fine detail, but focusing on one individual element could be difficult as everything seemed to fight for my attention. It was too mid forward, the sound stayed within the confines of my head (often focused in the middle of my forehead) rather than surrounding me, and I just found it fatiguing after fairly short listening sessions. I felt the SE846 grabbed me by the lapels and aggressively shouted in my face.
Or to put it another way, the UM Pro 50 is like laying in a warm bath, while the SE846 was like standing under a cold shower. It was invigorating, but not something I enjoyed.
With the UM Pro 50 I can focus in on individual detail quite easily and things don't all fight for my attention at the same time. If I want to, I can relax and let the music float over me. It can be used for detailed critical listening but it can equally be used for more relaxed easy listening thanks to a non-fatiguing, smooth, laid-back sound.
Not very long ago I was listening to an album I haven't heard for many years, using my UM Pro 50, listening to FLAC files, on a a high-res player. As I was walking I noticed the sound of people talking behind me and turned to see who it was, only to realise that no one was there and what I was hearing was in fact subtle background detail I'd never noticed when listening to the album before. But what impressed me, beside the fine detail retrieval, was the fact I'd been so convinced that the sound was coming from directly behind me. The UM Pro 50 can place sound in space like that. I don't believe the SE846 can.
I found the UM Pro 50 much better at positioning sound 360 degrees around and outside of my head. With the UM Pro 50 I not only hear instruments, I sometimes feel that I can "hear" the empty space between them (if that makes any sense).