I tried with the bridging but it didnt work. Here's what
the manual says:

1. The host requests data by setting RTS to L.
2. Upon data request by CTS, the PMD570 responds
by setting RTS to H if not busy.
3. The host checks if CTS is H and stats data output
on TxD.
4. When data output finishes, the host sets RTS to H.
5. The PMD570 checks if CTS is H and sets RTS to L.

The host is the RFX9600. This might be why the bridging
didn't work. The Marantz waits for the RFX9600 to lower
it's RTS and then reacts.

Hmm as i look this list now it doesen't really make sense.
I have to investigate this further.