Seeing I2S is a proprietary connection, you’d probably have to build your own, like here:
The Octave will not be budget, apparently around $6,000, and a closed system.
I am wondering what HD formats you are planning to use. I have a 4 x 4TB RAID QNAP, used for business, tried using it for audio and it struggled with 24/192 files. I bought a music server, but then bought a 4 x 2TB SSD QNAP TS473 for business for about £1,500 ($2,000) and it is dramatically faster.
Someone will ask what you have against a usb to I2S Matrix conversion. Otherwise sounds possibly like a complete rethink.