If you check with the manufacturer I think that there is a way to find out how the HDMI is wired internally to the contacts. That must be done the same way as the receiving Dac that accepts I2S. Some manufacturers use a proprietary contact scheme that is not universal to other DACs, therfore the "handshake" between the two devices creates an error. (If known which wires go to which pin on the hdmi you can wire your own hdmi cable). I successfully did it one time with an ethernet connection using cat6e cable I had lying around and it worked!
I have mentioned before in other threads that there needs to be a standard protocol for players and receivers that have I2S to all use the same wiring protocol so that all devices that have an HDMI/I2S input-output can talk to each other.
I have mentioned before in other threads that there needs to be a standard protocol for players and receivers that have I2S to all use the same wiring protocol so that all devices that have an HDMI/I2S input-output can talk to each other.