The Stellia is a touch better than the Z1R at resolving micro-detail. However, I agree that the Z1R has a wider and deeper stage, and has better imaging capabilities.Having compared my now-3+ year old Z1R's with the Stellias using a Dave yesterday i'd have to agree with everything you said ,except i didn't really find any area where the Stellias were better, then again i didn't really focus on the treble section.What do you mean by resolving though? I found the Z1R images a lot better,has better separation, the only area where the Stellia came out ahead was in lower midrange detail ,where it was slightly eclipsed by the bass on the Z1R ,but that's due to the tuning and i'd take it any day over the dry lifeless sound of the Stellia.They reminded me of my old audiotechnica m40x (tuning wise)
I also found the build quality and comfort lacking compared to the Sonys.
I think the best upgrade from a Z1R is adding a Dave to it
When I'm out and about (during my external auditions), the Hugo 2 has always served as my primary source.