Applying our sub to ST1

We discovered an inability to add our subs to our ST1 line, which is the audio from our videos. We have a Mac set up on ST3, and we can add or decrease the level of subs (which is set in a group) with no problem. But when we select ST1, we can’t alter the sound at all - any bass frequency is coming from the mains only. What am I missing?

Most likely lows ?

Seriously, is there any “sub-worthy” content in the video-soundtrack ?

What happens when you hook up the Mac to ST1 ?

Giga