for all Spotify fans out there take a look at this awesome project: https://github.com/Fornoth/spotify-connect-web
I installed it on my Raspberry Pi b+ with a digi+ and it works almost out of the box. I only had to change one line. Guess this is only necessary for the digi+ but here is what i changed, line 74 in connect.py:
mixer_volume = int(mixer.getvolume() * 655.35)
mixer_volume = 1 #int(mixer.getvolume() * 655.35)
Done! Now i can use Spotify connect with the hifiberry.
Of course you need a Spotify premium account and a Spotify developer key, but it's definitely worth it. Don't know if it is completely legal since there seems to be reverse engineering involved.
Should also work for the dac. Give it a try and don't forget to star the project on Github!