I just received my DAC+ (Belgium, no shipping track, delivered in 3 days, pretty fast !).
My RPi is under Gentoo, here is the kernel config I needed to configure (I don't have any module):
I can't confirm that all is required or if something is missing (except default alsa setup), but these are some changes I made to get it to work.
Here is pictures of my setup :)
Thanks for this product, it's just fantastic !
Gentoo + Rack Setup