I'm experience linux and pi person.
Installed the card, I have the hifiberry dac+ rca
I edited the comment # out of the correct line in /boot/config.txt
If I comment out the line for the the plus (the card I have), I reboot and get no options in the pull down to select the audio output (besides Headphone jack and hdmi, nothing for the card). The card does not show up if I type "aplay -l" from the command line and of course no audio comes out of the RCA jacks.
If I comment out the non-plus option and reboot, I get an option for the non-plus DAC in the pull down. The card will show up if I type "aplay -l" from the command line but no audio comes out. Mind you this is not the correct version to chose.
The download of RuneAudio is about two days old. I checked for updates.
Everything else seems to work, but no audio coming out of the RCA jacks.
Any hints ... well would be helpfu.