After one casual listen to Clearmountain's Sparkle Atmos mix, I'm pretty happy with it. Lots of guitars and keyboards in the side and rear speakers, plus some fun details up in the heights like the synth brass in "Waterfront" and the 'sha-la'la' backing vocals in "Street Hassle."
As expected, it is very different from the 2014 Steven Wilson 5.1 mix. On the plus side, the lead vocals in the center channel are more prominent and better-integrated with the rest of the soundstage. All the bass parts seem to be mixed discretely to the center as well, most notably at the beginning of "Waterfront."
There's also a bit more variety in how the instruments are positioned from song-to-song. The 5.1 pretty much always had the guitars in front and keys in back, but this version keeps you guessing. The first track has the keys in side right and guitar in rear left, then the arrangement flips for "East At Easter" with the intertwining guitars locked to the sides and big synth pads pushed to the back.
That said, there are some aspects of the 5.1 mix that I prefer. For example, a lot of additional vocal layers that SW put in the rears to very cool effect (like the double-tracked 'I will be there...' in "Up On The Catwalk" and 'run till we come...' harmonies in "Speed Your Love To Me") are now upfront instead. I also really liked how the big drums were spread out all around you, in both the front and rear speakers, whereas they seem more weighted to the front in the Atmos mix (though the cymbal crashes in "Waterfront" are elevated into the front heights, which is pretty cool).