There are several settings for the Digital Output on the GNX-3. In the UTILITY section, you can choose between 4 different output modes for the S/PDIF output. The options are as follows:
GTR + REC = You will hear the Guitar and Recorder sections mixed together at the Digital Out.
G-DRY = You will only hear the Dry guitar signal only (no effects) at the Digital out.
G-AMP = You will hear amp modeling, cabinet and noise gate only (no effects).
RECORDER = You will only hear the recorder section at the Digital out.
In order to hear your recorded tracks out the S/PDIF output, you will need to choose either GTR + REC or RECORDER in the Digital Output Configuration page of the UTILITY section.