HDMI/I2S to USB or RJ45 I2S port

Just curious about something re I2S and dacs I came across today while surfing the web. I notice some dacs use a USB or ethernet/RJ45 input port for I2S rather than an HDMI style one. Let’s say one has an Oppo 203 with an Oppomod HDMI/I2S card, as I do, or something similar. How would that work (or not) with such a dac: a connector adapter or something more complicated or not at all? Examples that I came across are the Aqua Acoustic Formula XD, Fore Audio DAISy and the Brinkmann Nyquist. Thanks,