Hi,
I'd suggest that you use your Mix Outputs 1-16 of your StudioLive 32 III to connect to the Dangerous 2-Bus+
This will allow you to send multichannel audio back from your computer via USB and then easily sub-mix the tracks to send on to the 2-Bus+ You could then bring the stereo main output of the 2-Bus+ back into the Aux Input 1-2 (for example) on the SL32 III if you want to record the summed output of the 2-Bus+