Apple does not support UPnP device discovery. Your easiest method to connect with a Mac is to directly connect to the Director via ethernet cable. The default IP address of the amp is 192.168.0.249.
You will need to give your computer a static IP address in the range of the Director in order to communicate with it.
Change the IP address to 192.168.0.X – X is a value between 1 and 254, but do not use 249, because that is being used by the amp.
You can also use a network scanner application which will list all IP addresses on the network along with the devices corresponding MAC address. You can then cross reference that list by getting the MAC address off the back of the Director amplifier to confirm if it is on the network or not.
Director Amplifier Home Page