As I'm breaking in my new NW-WM1A, I've been switching between the Space One and the H9. The thing that sticks out at me soncially is that the H9 is more "relaxed" if you will. The Space One is a more up front, lively presentation which makes it appear to have more detail and resolution. The H9 does have good low bass, but you don't feel it in the same way as the Space One (think Moog Taurus pedals). The H9 does have good detail - make no mistake.
The 1A drives the H9 better than the ZX1, so it's been easier to do comparisons. I added a touch of EQ on the 1A for the non-DSD files and it's amazing what a tweak here and there can do. At first blush, you may think the sound of the H9 is more "flat" in comparison. A good example is the album "All the World's s Stage" by Rush (new 2015 192/24 mastering). But it's not, really. Once you account for the slight volume difference between the two, they're more similar than different in many ways. The differences are interesting, but none are "deal killers", so it boils down to preferences in what you like in terms of sound.
If I can equate it to anything, the Space One is more like listening to all solid state and a clean signal chain while the H9 is warmer - not quite an all tube setup per se, but those kinds of sonic differences are how I'd characterize them. Warm tends to have slightly less accurate but pleasing bass ("wooly"), whereas solid state can have lots of punch but may not be what you want for all kinds of music.
It's been interesting because both have pros and cons. Having used the Space One on very long flights, I know it's not fatiguing, but I can tell the H9 definitely would not be.
Just thought I'd update my impressions.