For me, the Z1R and 1Z was underwhelming at best - the bass was flabby and lacking control, the mids were uneven, and the top end was piercing. The headphone lacked dynamics overall and technical merits were soft and lacking. Wasn't as bad as the MDR-Z7M2, I grant you that - that was even worse. Both of these headphones can scale up and sound decent being driven properly, so I'm assigning blame here to the source.
When I had these DAPs, I did my best to generate more power by stacking them with various portable amps (CV5, BA300s, Fostex HP-V1, etc), but because of the lack of line-out it never sounded coherent. Given Sony are using the same tech here, I suspect they'll continue with the lack of a line-out.