There is a Denafrips tutorial on YouTube for changing the pin-out configuration of the I2S input. I think it's 0-0-0-0.
Matrix Audio settings offer a few choices and I used setting "A" .
And as I said in my earlier message, the recent Matrix firmware update caused some streaming stuttering if using a WLAN connection. I changed to a LAN connection and this corrects the problem.
So for now, WLAN isn't really working. Maybe they'll fix it eventually with a firmware update. Matrix and Apos both have pretty crappy service.