The zero has/had problematic qc issues, and while the dac is nice i don't think the headphone amp is good in it at all.
The aune may have minor(meaning very easy to fix) qc issues, both the dac/amp of it is good for the price. However, it really needs a better power supply, that's the weakest point in it imo.
Both of these units can be "diy"ed , through-hole components are easy to work with, and you can change opamps to make it suit your tastes. The aune has more quality components (capacitors, volume pot etc).
The headroom feels too commercial for my tastes... also it has batteries, usb charging etc... it's not a desktop design.
But ultimately, choose what you like.