Metrum used to make an Ethernet to i2s bridge at one time.
It was their recommended route to connect to an accompanying Metrum DAC with i2s input.
No idea what protocol or cable end they used but might be worth looking into.
https://www.usaudiomart.com/details/649629340-metrum-acoustics-ambre-roon-endpoint-streamer-with-i2s...
Sold but gives you an idea for research possibly.
It was their recommended route to connect to an accompanying Metrum DAC with i2s input.
No idea what protocol or cable end they used but might be worth looking into.
https://www.usaudiomart.com/details/649629340-metrum-acoustics-ambre-roon-endpoint-streamer-with-i2s...
Sold but gives you an idea for research possibly.