Multiple VSTi's in a rack

[ortseam]

simply let me add 2 VSTi's into the first two slots of any rack and understand it and hence treat them equally. Like any other DAW I know does...

Not as simple as you think in fact. Different VSTi's have MIDI/audio routing organized differently. Some pass MIDI through, some not. Some have audio inputs, some not. Some have multiple audio outputs, some not. Placing two arbitrary VSTi's sequentially in track FX slots may cause confusing results in any DAW.
With MUX you can clearly see how your MIDI/audio signals pass and manage everything exactly as you like. I see no disadvantage here.

[Odd Fella]

simply let me add 2 VSTi's into the first two slots of any rack and understand it and hence treat them equally. Like any other DAW I know does...

Not as simple as you think in fact. Different VSTi's have MIDI/audio routing organized differently. Some pass MIDI through, some not. Some have audio inputs, some not. Some have multiple audio outputs, some not. Placing two arbitrary VSTi's sequentially in track FX slots may cause confusing results in any DAW.
With MUX you can clearly see how your MIDI/audio signals pass and manage everything exactly as you like. I see no disadvantage here.

Then why do other DAW's manage to recognize what they are dealing with?

In terms of disadvantages, for instance I need a couple of clicks to get to the GUI of one of the VSTi's, because they are not in the rack at the bottom as usual.

[ortseam]

Then why do other DAW's manage to recognize what they are dealing with?

In terms of disadvantages, for instance I need a couple of clicks to get to the GUI of one of the VSTi's, because they are not in the rack at the bottom as usual.

Got your point. Agree. Maybe it really would be better if RACK module had it's own modular area when you could setup every slot input/output routing so that any problem of that kind could be solved easily and any VSTi GUI could be reached in one click.

[Calum]

There also is a preset called "Multi Synth Rack".
It's in MUX Factory Library -> Instruments -> Templates.
You can insert that in a rack slot and there you can easily layer up to 4 synths.
That preset also is fully editable of course, both the modular patch as the front panel layout.

I don't see that in M7, which I am still using.
If it is a new rack, can I copy it from M9 to M7? I.e. are they compatible?

You can recreate the M9 Multi Synth Rack in M7. Minimising the rack and instruments into the Floating Windows Bar gives one click access to the instruments:

[Odd Fella]

Thanks, will watch it tomorrow in slow motion