Well it should be possible to install an LVDS/I2S interface board into an Okto DAC. This is what you need -But it’s still interesting to find a diy solution for this.
https://www.audiophonics.fr/en/diy-...ipi-receiver-hdmi-to-i2s-dsd-dop-p-13981.html
You would connect this board's I2S output connections to the I2S input of the Okto main DAC board, displacing the connection from the existing USB interface board.
But of course you might not wish to permanently disable the USB interface, so in this case you might wish to make the connections swappable via headers, or there's a digital data switch board available from Twisted Pear Audio -
http://www.twistedpearaudio.com/control/otto.aspx
It might be worth asking the Okto people for advice. An earlier release of the Okto DAC was a DIY module, so I think the Okto developers are open to custom requests.