last week I tried volumio again, and was happy to find airplay was working 
but then after a day it just disappeared. I’ve been banging my head last week trying to solve it. I knew it could work and now I want it!
after searching the forums and rebooting, rebuilding, rewriting the sdcard with a fresh image, still nothing
then my new router arrived and I just let it be, but after I configured my new router Airplay popped up 
so it had to be something wrong with my original router, and I searched for anything that could be changed.
well it seems that when my router is reboot, it resets some setting for my wifi!
when I disable WMM for wifi, Airplay works, when I reboot WMM is set to enabled AIrplay stops working.
hope this helps someone and save you your time.
cheers.