MR816X WDM Digital Output

Hi - I am trying to get WDM audio from my PC to a digital output on my MR816X. If I set the WDM Audio Routing on the Yamaha Steinberg FW Driver to an analog output on the MR816X, it works just fine. But if I set the WDM Audio Routing to digital (either coax or optical)., I get nothing. Does anyone have any suggestions?

To what is it connected?
Never had any problem with AES3 or SPDIF on coaxial or optical outputs.