Copy your mt-daapd.conf to mt-daapd2.conf.
edit mt-daapd2.conf, and change the following values:
general/port (to anything different, but between 1024 – 65535. I use 9999. No reason, just do.)
general/db_parms (I’d change it to /opt/var/mt-daapd2)
general/mp3_dir (to wherever your other music is)
general/servername (to whatever you want it named).
Then do “mkdir /opt/var/mt-daapd2” (or whatever dir you used), and “chown nobody /opt/var/mt-daapd2”.
Then go ahead and run it: “/opt/sbin/mt-daapd -c /opt/etc/mt-daapd2.conf”
Wait for it to index, and see how it works.
Check your syslog if you see any problems.
And yes, the web-root is the base of the web pages for the web admin — those can be the same for both instances.