Ok, I have finally managed to understand better.
Here are the steps to make mt-daapd work with SELinux enforced (yes, I forgot to mention that I ran in permissive mode earlier, which explains why everything seemed to work!):
# setsebool -P allow_execmod=1
# execstack -c $(locate libFLAC.so.7)
# execstack -c $(locate libavcodec.so.0d)
In the first line, you turn on execmod; in the 2 lines after, you disable the execstack from shared librairies.
Nice. I’m going to sticky this until I can put it on the wiki. Thanks.