I think I might have a solution, but it is not the best.
Start by saving a scene with the faders at the volume you want.
Then save another scene with the faders that you want to fade out at the volume you would like it to end up at.
Once you do that you can set your soft keys to activate those scenes.
Then to make it fade for a certain amount of time use the “crossfade time” feature on the scenes.
I hope that helps and that works
