Nomax if you are mainly after power and sound quality obviously get a Lotoo Paw Gold : 500 mW @ 32 ohm. Definitely will drive all your headphones.
Isn't LPG Class A amplification ? And the battery won't even come close to Walkman WM. Class A efficiency is only 30%, and class D is 90%...hell...if done right....100%. That means if we are talking efficiency alone, the 250mW per channel could be multiplied by 3X times to class A. Logically would be 750mW per channel from WM Walkman in comparison to class A .
Class D wiki
https://en.m.wikipedia.org/wiki/Class-D_amplifier
Class A
http://www.electronics-tutorials.ws/amplifier/amp_5.html
If you listen to DSD 256 especially in balanced mode on the WM series Walkmans battery life will not be longer then 15 hours, an maybe shorter if you go full volume.The Paw Gold is the only one that can deliver the promised playback time at full volume on DSD 5.6 MHz.