I was indeed referring to the "Digital Gain" setting found in the LiveStack's Alignment tab. Same for the "Black level" setting, this is the one under the Alignment tab.
These are the parameters that Sharpcap's star detection algorithm will use: as far as I understand, it takes the input image from the camera, thresholds it using the above "black level" (essentially trying to remove the sky background in doing so), applies the "digital gain", then tries to detect the stars with that pre-processed image. Maybe the Digital Gain comes first, then the threshold, I don't know...