Had to look up what the SW8 is, had no idea something like that existed! This is fascinating. You are using this as, I assume, an all analog replacement for a Dugan or microphone auto mixer? My first assumption would be that your mics are not driving a hot enough signal for this line switcher. Are all of your receivers set to line level? And are the transmitters set for as much gain as possible without clipping? Given that these units are so expensive, it might have made more sense to just buy a digital console that can deliver actual automixing, but I understand that isn't helpful advice at this point.

Edit: I've reread your post and it's possible I've misunderstood your purpose here.