Thanks @soix
I was kind of expecting that. I have found a Sonnet Morpheus Dac which has the RJ45 I2s rather than the USB. I was leaning towards an Aurender streamer but they mostly have USB.
I'm glad you told me of the lack of standard for the I2s as well. If I understand correctly even a streamer with an I2s output won't necessarily be compatible. I believe Sonnet has planned to use the I2s with their streamer which is a Roon end point only (I think)