Re-reading your message, I now realize your confusion about how the repeaters work.

Each box comes with two devices: A transmitter and a receiver.

Transmitter: Looks for the IR signal from your remote, encodes it, and transmits that encoded signal with radio waves.

Receiver: Listens on the radio waves for the encoded signal, decodes it back into IR pulses, and sends those pulses out as IR signals from its face.

So to do it bidirectionally, you'd use two sets.