PBX does not need to run on a client - only on master and media servers. Verify that vnetd (1724) is still open (bi-directional) between master & client and media server and client.

With older NBU versions the dozens of processes connected directly to each other. In heavily firewalls environments (like the one I'm in) this is a nightmare to manage. So, for me, the biggest advantage to PBX is that I only have to open a few ports and not every single port for e wry single NBU application. PBX handles transporting the connections over it's session to the client and media servers, and even to the master. Makes firewall life way easier.