The EtD with the conductor card that has been flashed with the conductor firmware sends out sync pulses to keep the slave in sync.
The conductor card adds a compact flash card adapter, mp3 adapter and a real time clock to the EtD. The slave card just adds the compact flash card adapter.
The data sent out on the Ethernet by the conductor does not contain channel data. It is composed of synchronization data - I'm guessing, but I would assume sequence # and frame # type data in a multicast packet. That way you could have as many slaves as you want... Listening... Playing their own sequences based on the sync packets they receive...