-Unicast method means that the client will be routed through the network to the chromecast and everything should work as peer-to-peer communication (i.e. if it is the same vrf, you are already done configuring). If you have a firewall separating the "office network" from the "Chromecast network" you need to make sure that the client is allowed to contact the Chromecast through the firewall (chromecast uses ports usually ranging UDP/32768-61000 and TCP/8008-8009). For Apple-TV or other mDNS-devices it might be other ports and you need to sniff the traffic or google the used ports for that specific mDNS-device.
-if it uses multicast traffic for transporting streaming/data you will first need to make sure that your network supports Multicast routing and then also make sure that the traffic is allowed through any firewalls that separates the networks.