If you just wait AirPlay, installing shairport-sync on Raspbian shouldn’t be too hard. The tutorial written by Andy Jenkinson looks slightly old but should still work fine.
Was about to suggest basically the same thing. I had some success with Shairport Sync built on top of Raspbian Jessie Lite.
I’d ignore the:
rpi-update
step from that guide though. It doesn’t update your firmware, it moves you to a bleeding-edge firmware which unless you’re trying to fix a specific problem ( or know what you’re doing ) will be more trouble than it’s worth!
Oh regarding Volumio, it’s apparently possible to just update it to the latest kernel so it’ll boot in a Pi Zero, you need an older Raspberry Pi 1, pop in the card and run:
sudo apt-get update
sudo apt-get ugprade
( I’m assuming apt-get upgrade will work as a more sensible stand-in to rpi-update )
I don’t think it makes much difference, but just in case you paint yourself into a corner setting up pHAT DAC and want to re-image your Pi, I’d say it makes sense!
If you run into any troubles, I’ve got a working setup somewhere so I should be able to help.