You have quite a complex goal, so maybe think of it by sub-dividing the elements into different pots.
I’m also unsure if the plan is to, say, have four Scalers playing a backing whilst you are connected to a fifth and play along with some bound keys (as @ClaudioPorcellana) or some other plan. This important because the means to trigger new songs will vary depending on that setup.
So I thought I’d just set up a quick Omnisphere / Scaler set up as one of the building blocks, as you can feel up to 8 Scalers into a single instance. Further, it allows you to lock patches into RAM, which otherwise would be loaded from disc. This opens up the possibility of doing a patch change at the end of each song instead of having several Omnisphere instances.
The overall test looks like this
The ‘scaler pad’ and ‘scaler perf’ each has a scaler instance. For the scalers I chose a simple progression from the common progressions, ‘Triumphant Thickened 2’
For the second scaler (‘perf’) I chose a performance of ‘Chordal Perf 2’ as the melody line.
As you are aware, the output by default goes to audio, but we can insert a ‘dummy’ midi track to ‘hop’ it over to the synth. This is done by ‘midi hop pad’ and ‘midi hop perf’.
Now set up a fifth track for Omnisphere and load it in. I put a string patch onto channel 1
and a D50 piano into channel 2
You can now control the relative channel volume in the Multi Mixer section
Now just a few small tasks to link it together and trigger it. First, link the dumy tacks to Omnisphere (note the routing is done in the sending track and not the target track to get the many to one setup)
Put a dummy midi clip on the scaler tracks 1 and 2, by right clicking in the track
You can see then here …
Now in the scalers switch the internal scaler synth sound off, and in settings put DAW sync on
Now trigger the play back in the master track and adjust the track 1 and 2 volumes in the Omnisphere Mixer, and there you have it.
Now, what you could do is add a scaler track with midi input from your keyboard controller and bind the progression. You can either use a scaler internal sound routed to the master out or add a dummy and route it to another Omnisphere patch, trigger the start from your keyboard and play along.
Obviously all this isn’t where you want to be yet, but it maybe gives some ideas. The then challenge is to deal with changing songs and the best setup for that. It may be that Cantabile solo can do that. Also, some routing may be easier using dummy external midi ports, allowing you to control things better by using the ability of scaler to specify the output channel.
I’m not sure if this was of any use - perhaps you were completely familiar with this, in which case apologies…
You can download the Ableton ‘als’ file at https://btcloud.bt.com/web/app/share/invite/Inbt6uNvhU