how to mix scenes together, and make staggered entries and offset different long fade start (urgent)

[Bennnid]

Hi Izadorables, 
I have a patch with an activated scene in the background receiving
- matrix value for light dmx
- matrix value for sound volume
- listener for medias selection

So I use  scenes crossfade to mix between different state, 
but sometimes the operator would like to send a fade of 10 sec on a Chanel and just 5 sec after, a 20 sec on another one,
- I could set some envelopes for that but I don't want to make a mess in the patch ( more than 100 cues, and stage director often needs change the Q really fast)
- I could activate a +1 scene with a keyboard watcher allowing fades to be performers offset during the same period, but then jump and deactivate previous scene doesn't make it less complicated than envelop use... ( operator mainly use space bar to launch Qs and I don't want to make a mess with a bunch of control.. Is there a "space bar config" that will jump after last activated scene and deactivate all of the previous ( but not the main backgrounded activated scene with receivers ) in a one touch ? 

what do you think? how would you achieve that for an operator that doesn't want to enter the patch 

thanks

[DusX]

@bennnid

Perhaps you can send the Current scene value to the background scene, and switch between behaviours in this way.
You would program follow controls for each scene (if current scene is a match) which would run after receiving the current scene value.