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.
I don't get why this comes up again and again, even if several people disproved it as wrong so many times.
That is totally unrelated to its output power. If you don't like the Sony sound, you don't like the Sony sound. Its a matter of taste but its unrelated to output power.
If you prefer other devices which sound very different from the Sony Sound (but also happen to have higher output power), they sound different because they sound different, not because they have higher output power.
Take the M17 vs WM1Z as an example. 3000mW @ 32Ω vs. 125mW @ 32Ω
M17: Boring, flat, lifeless. Makes acoustic life recordings sound like Monitor Recordings.
WM1Z: Exciting, unique and fun sound that makes acoustic sound like you're actually there in the concert hall
The M17 does have 24 times the power and sounds extremely boring, especially when paired with the MDR-Z1R. The MDR-Z1R+M17 is not a good combo. The M17 completely fails to make the Z1R shine. The HD800S or HD820 are much better matches for the M17 than the Z1R. I would not get this headphone owning that DAP.
You see? With 1/24 of the power you can make the Headphone sound better.... if you like the sound. Some people don't like the Sony sound and that is absolutely okay. Its a matter of taste and not everyone is into this exciting/life like sound. I personally don't understand why, maybe some people just hate how instruments sound in real life, but thats a different topic. It is no use to discuss about taste.
But, and that is the important thing here, this is totally unrelated to output power. The WM1Z would not sound any different with 2500mW.
M11 Plus LTD --> 588mW
M17 --> 3000mW
They sound almost the same. In a blind test, its pretty much impossible to pick them apart.
You see, your issue isn't power, your issue is that you don't like its sound (no matter the power).