Better Internet Sharing
Mac OS X (I'm speaking here of Lion, Mountain Lion &amp; Mavericks) is a pretty good system to build a secured network access. But I can't agree more with your analysis: it really lacks any GUI to manage configuration.

For example, to be able to manage correctly DHCP, I finally set up a
highly inelegant way to circumvent the way InternetSharing is blocking any attempt to configure it.
This method may cause problem with any MacOS X update, so I have
to remove my modifications before any OS update.

Here is the technic I used with a solid success on a small network: How to stop InternetSharing overwriting /etc/bootpd.plist .

I haven't yet tested my /etc/bootpd.plist to enable distributing IPv6
addresses, but I'm pretty sure it would be working by defining the
correct &lt;key&gt;net_range&lt;/key&gt; entry.