Stereo version:
All connectors use the same left/right channel pair.
AES/EBU 1 = FL/FR, Left/Right (stereo)
S/PDIF 1 = FL/FR, Left/Right (stereo)
TOSLINK 1 = FL/FR, Left/Right (stereo)

3 Multi-channel options:

Each connector has 2 channels.
S/PDIF 1 = FL/FR, Left/Right
S/PDIF 2 = C/LFE, Center/Sub
S/PDIF 3 = SL/SR, Surround Left/Surround Right
S/PDIF 4 = SBL/SBR, Surround Back Left/Surround Back Right

And the last available option:
It supports 8-channel audio via USB output. The board also has two additional BNC jacks, one SPDIF output and one SPDIF input. The output is connected to the USB interface for audio monitoring or synchronization of other external devices. The input can then be used as an alternate signal source and switched between HDMI/ARC/SPDIF/IN for more flexibility.