I8S is basically an 8ch TDM, left justified with a 50% duty cycle on the LRCK signal.
Not all devices with multiple DIN/DOUT pins support it.
You need to search for TDM,TDMCA or DSP interfaces on the converters used.
The devices you mention all support TDM, and thus, I8S.
There is no formal I8S format... it's a term thats used by other semiconductor manufacturers to describe a data-packed I2S like stream.