A few things to consider:
A) Make sure that the Digital input format is set to the type that corresponds with your signal source. Choices Are: AES, SPDIF Coax and SPDIF Optical
B) The default routing on the Hilo delivers signals from the digital input to Record 3+4. In your DAW, make sure that the input selected is 3+4.
C) Make sure that the signal source is operating at the same sample rate as the Hilo. Either both devices should be clock sync'ed to each other, or the Hilo should Sample Rate Conversion turned on (from Settings > Audio).