A decoder can only be routed to one encoder at a time. You can't have one decoder sending an Audio Return Signal to multiple encoders, for example. 

A lot of sites utilize CEC for volume adjustment/control of source and sink devices, this unfortunately can only be done when the encoder and decoder are in a unicast (or point-to-point) connection mode. You cannot get CEC passthrough to work reliably in a multicast AVoIP network. 

For the encoder, the encoder will output the returned audio via TOSLINK or HDMI strictly depending on how the decoder is "receiving" the ARC/eARC audio. If the decoder is intaking via TOSLINK, then the routed encoder will output via TOSLINK, if the decoder is intaking via HDMI, the encoder will output via HDMI.

Note - in the API commands below, remove the [] around the encoder/decoder ID/MAC

Establishing an Audio Return path is quite simple, here's the direct API commands:-

config set device arp enable [EncoderID/MAC] [DecoderID/MAC]

eg config set device arp enable 188A6A02118B 188A6A0213C9

This command will activate the Audio Return Path (ARP) feature, and establish a connection to the specified encoder & decoder.

config set device arp disable [EncoderID/MAC] [DecoderID/MAC]

eg config set device arp disable 188A6A02118B 188A6A0213C9

This command will simply kill the previously established ARP route on the specified encoder and decoder, and disable Audio Return (device will reboot).

config set device arp input [hdmiout, spdif] [DecoderID/DecoderMAC]

eg config set device arp input spdif 188A6A0213C9

This command will change how the Decoder ill intake audio from the sink device, either via TOS (spdif) or HDMI output. As mentioned above, this affects how the routed encoder will output the audio.

config set device forcearc {on,off} [DecoderID/DecoderMAC]

eg config set device forcearc on 188A6A0213C9

This command will give you the ability to force the decoder to only accept ARC audio, and not eARC. This is quite useful for systems that have an eARC compatible display, but only an ARC compatible AVR.