Check to see if there *is* an /opt/etc/mt-daapd directory… might look something like this:
foo@slug:~$ cd /opt/etc
init.d mt-daapd openssh rsyncd.conf sudoers wgetrc
libao.conf ntp profile rsyncd.secrets termcap
foo@slug:/opt/etc$ cd mt-daapd
foo@slug:/opt/etc/mt-daapd$ nano mt-daapd.conf
so “cd” is change directory, just like dos. “ls” is dir, with “ls -l” even more like dir — shows file length, etc.
There really ought to be an /opt/etc/mt-daapd, and it ought to have a mt-daapd.conf in it.
You could always fall back to something like:
find / -name "mt-daapd.conf"
which will search the whole file system for the conf file.