What exactly is the command that you used when you tried to run mt-daapd?
If you run it maunally mt-daapd expects a single parameter, the location of the config file.
So if your config file is in /usr/local/etc/mt-daapd.conf this should be like:
mt-daapd -c /usr/local/etc/mt-daapd.conf
If you did it like that, then probably your config-file isnt world-readable.
chmod 755 /usr/local/etc/mt-daapd.conf
(This isnt 100% water-proof, from a security point of view, but it should do for testing some stuff on a local NAS)