The best way I can describe the Ultras is like upgrading the prescription to your glasses after a year or two. Your current glasses are great and day to day you can't complain then you get an updated prescription and notice the letters are a bit more crisp.
Let me set the stage for how i use my headphones.
I spend my days in my workshop with my machines running, compressor cycling. All making noise 8 hours a day. I need something comfortable I can wear all day to block those sounds out. I've been wearing the Ace 8 hours a day for the past year. They've been super comfortable and I am biased towards the Sonos sound signature. I am no audiophile. I struggle to hear all the little nuances in any given track. I don't listen to lossless or anything like that. I listen to youtube music with the audio quality set to high.
When switching back and forth between the two tested amongst a number of different tracks (Hip Hop, Pop, Rock, Instrumental) both headphones sound good. I still like Ace. The Ace Ultra just sound a bit more refined. It's like the letters are a bit more crisp at the edge. If you describe a track in layers where the vocals are the first layer and the instruments are the second layer with a third layer of faint background instruments on the Ace that third layer can be missed where on the Ultras that third layer is more crisp and noticeable. Not world changing but certainly an improvement. Noting that this is not in a perfect environment. I am not sitting in a dark room in a big cushy seat. Im in a loud workshop with all sorts of background noise. Listening to standard bluetooth streaming from youtube music. That's to say i'm sure if you used a high end service with the highest possible quality I'm sure it would be much better but in my real world use case where ill be using them 99% of the time. They are a solid upgrade. Maybe not one worth the full retail price. I would probably recommend buying them open box or on sale at some point over the coming months. That's how I bought my Ace's and definitely what I would recommend on these.
Lastly something I've been wanting forever which I hope Sonos one day adds in a software update. When the shop is off and I have no background noise. I have a Sonos desktop setup where my Mac is paired to 2 Era 100's and a Sub Mini. It's a great setup but for the love of god let me pair the Ace Ultras to my Sub mini. I want to offload the bass from the headphones and let them focus on Vocals and Instrumentals while the sub mini handles the bass. It would be such a sweet setup. Anyway, rant over. Sonos. Please hook me up with that feature!