I don't think the send methods are documented any where. It's a bit technical, but here's a a quick overview:

unicast: The audio data is sent directly to a single player (via UDP on the player's ip address). Disables synchronised playback.

broadcast: The audio data is sent to everyone on the sub-network (via UPD broadcast on the broadcast-address). Sync playback is possible.

multicast: The audio data is sent to everyone who is within within 1 router hop of the tRio server (multicast on the multicast-address). Sync playback is possible, but is more of a problem in wireless set ups.

Cheers
Paul