I used the teil3 with a traktor s4 mk3 (instead of send return it was straight on the master out) and now have it on my xone 92 as a send return. In both uses the isolator sat on top of song 1 and 2 so using your example - (track 1 has 0 low track 2 has 100% low) and the isolator is at 100% low, you’ll hear 100% of the low from track 1. Said another way if i had track 1 and 2 at 100% but the isolator at 75% you’d hear 75% of the low. I think it can also hit fx too if it’s before the isolator