Spent some time with MDR-Z1R and the 1ZM2, and I can say this was the first time I experienced the larger Z1Rs being adequately driven by a Sony portable DAP, both in terms of power and tonality.
High gain - 100 hit the spot. The MDR-Z1Rs on the original 1Z always felt a little compressed and sibilant due to the infamous peak in the highs. Between the IER-Z1R and the MDR-Z1R, i'd be using the IEM variant 95% of the time.
Happy to say on the 1ZM2 this peak has been smoothed out. I can finally see myself getting much more use out of the headphone version. Glad I held on to them.
Similar to
@twister6's experience. The sound clears up significantly after you get into the double digits of hours played. Bass becomes tighter and more dynamic, yet retaining an appealing decay.