Denafrips told me not to do this, but I might try this, as I can do the same.
You’ll most likely break your DAC if you try to connect the HDMI output of the Oppo to the I2S input of the Denafrips.
Just because they use the same connector doesn’t mean the wires are carrying the same signal.
I2S pinouts using the HDMI connector are different for each manufacturer. There’s no single agreed upon standard.