I am working in a situation where I am running shows that have multiple microphones, and multiple speaker output channels. Right now, I am using a Soundcraft GB4 and a MacBook Pro equipped with Thunderbolt, USB 3, and a 3.5mm audio jack with optical audio support. I was wondering if it would be possible to hand control of all microphone inputs and speaker output to the computer rather than doing it on the board. Since this mixer doesn't seem to support running cues alone, it would be nice to let Qlab handle adjusting Mics and output. Right now, I'm just using the 3.5mm audio jack to output cues from Qlab to the mixing board, which then plays the sound on a set of speakers.
This is not possible with the Soundcraft mixer you are currently using. This mixer doesn't offer any external control interface.
It should be possible if you buy an audio interface connected to your MacBook Pro that has sufficient inputs and outputs as the Qlab documentation mentions basic control of inputs and outputs of an audio device.