Hi. I don't have an SL desk but I looked at the manual. Unfortunately, as I'm sure you'll know, unlike Studio One, the mixer doesn't have a sidechain ducking feature on the gate (which is what you're after). The work-around (and this is in the manual) is to use the compressor with a sidechain. So, you'd use the channel your click is on as the feed to the compressor. The compressor will be inserted on whatever channels or buses are feeding your IEMs. I've just tried it in Studio One and it works a treat. I was able to completely silence a track with some music on it when a click on another track was present. When the click was not present, the music returned. Should work for you too. It was easy to find the right settings on the compressor to make this happen. Hope this helps.