So after spending 30min or so with A/B testing of ZX507 and WM1A (direct source on for both) with IER-Z1R iems I can say the following:
- Couldn't hear any audible difference with single ended output on same volume and different tracks. I used "Ultimate Headphone Demonstration Disk" as Hires for full range sound and "House of Zef" from Die Antwoort for bass heavy tracks.
- WM1A has significantly more power left. 75 volume setting in low gain matched at 100 on ZX507.
This again confirms that volume matching is key for any comparison. And all the nice audiophile lingo heavy comparisons "out of memory" are often just pure crap if you start digging deeper and identify multiple influencing factors.
If you need streaming out of the box - take ZX507.
If you want solid battery life, more power, USB DAC and Bluetooth streaming - take WM1A.
This is not an easy choice for me now... I was hoping to improve my overall situation by sidegrading to ZX507 but now I miss Bluetooth streaming and think that carefully curating the music saved on DAP is part of the experience. Tidal and Plex in DAP give more flexibility on the other side. Decisions, decisions...