How to edit /etc/minidlna.config on a Mac

Which Duo, a v1 or a v2? See How to tell whether I have a Duo v1 or Duo v2 or NV+ v1 or NV+ v2

Duo v1 is Sparc and Duo v2 is ARM. Since you're talking about restarting ReadyDLNA service I assume you have the v1.

You can install the Sparc EnableRootSSH add-on: http://www.readynas.com/?p=4203

However do pay heed to the warning:

NetGear wrote:
With the EnableRootSSH add-on, you can now remote login to the ReadyNAS RAIDiator shell as a root user. Initial password for root will be the same as the current FrontView admin password. Please keep in mind that NETGEAR may deny support if you’ve enabled root access.

To be able to use SSH you need to install the Sparc EnableRootSSH add-on (there are other addons to enable SSH access but these are for support use only).

On Sparc installation is via System > Update > Local

Username is 'root' and password will initially be set to be the same as your 'admin' (Frontview) password.

You can login using PuTTy (free program you can download) on Windows.

Alternative you can use the Terminal (found at Applications > Utilities > Terminal on Mac OS X) on Mac OS X or Linux:

ssh root@ip.address.of.nas

Then use Linux shell commands.

If you wish to change the root password you can simply use the passwd command:

MDGM-NAS:~# passwd
Enter new UNIX password: 
Retype new UNIX password: 
passwd: password updated successfully

As for using the "vi" command take a look at its MAN page (google search for it on the web)