This step is not necessary, but it seems like a good idea if you have Mac computers.
/etc/avahi/services/smb.service with the following content:
<?xml version="1.0" standalone='no'?><!--*-nxml-*-->
<!DOCTYPE service-group SYSTEM "avahi-service.dtd">
The service that contains
<txt-record>model=RackMac</txt-record> is only there so that on Mac computers the NAS shows up as an XServe server.
Enable mdns and the avahi-bridge-dsd service:
svcadm enable dns/multicast
svcadm enable avahi-bridge-dsd
I had to reboot the NAS after doing this before MDNS started working and properly advertising.
This is how the NAS appears on the Macs: