I just got a Raspberry Pi 2, Hifiberry dac plus, edimax wireless adapter. Installation was smooth and the system was great and smooth with excellent audio playback.
But i could not get WIFI working, i am using WPA 2 TKIP and i could not connect to the wireless network at all from webUI and also thru manual options like editing /etc/network/interfaces etc. Other systems like OSMC and Openelec have this feature. It would be awesome if Volumio includes this feature by default.
Volumio has this in the network settings page. It works for most people.
There is a chance that your adapter might not be supported. And make sure that you have a good signal during first setup.