I had a look at number 3 and this actually might be the best option. I never actuallt used midi sends before so I can see you can select a MIDI send destination for each channel (it seems I only can use 4 channels which is exactly how many I need for 4 voices). This means I can actually deactivate the output routing for that midi channel and only use the midi sends each routed to a seperate instance of my piano VST . I can also then keep all 4 voices in the same midi part as I have now. So that appears to be the top solution for this.
Keep in mind that that the MIDI Part(s) you are using for the score doesn’t need to be the same one you use to play the VSTi’s.
For example, you could create 4 Instrument Tracks for SATB voices. On each Track’s VSTi set the Instrument itself to only play Channel 1 on the Soprano VSTi, Channel 2 on the Alto, etc. Also make sure that the MIDI Channel setting on each Track is set to “Any” and not a number. Next create an empty MIDI Part on the Soprano Track. This is the MIDI Part you will use in the Score Editor. Then copy this Part onto the other 3 Tracks making sure they are Shared Copies - now any change you make in one of these 4 Parts will occur in all of them. When setup this way you can edit all 4 voices from within a single MIDI Part. And while the MIDI Parts on each Track will contain the notes for all 4 voices, only one of those voices will play because the VSTi is only listening to a single Channel.
On my VST piano instrument where do you set the instrument to play on a certain channel? This is an option inside of Halion but not on my Grand Rhapsody Piano instrument.
I don’t know anything about that specific instrument - and the implementation would be provided by the VSTi & not Cubase. Is your piano a self-contained VSTi? All the major instrument platforms like Kontakt, Halion, Play, etc. let you specify the Channel - so if it is one of those you should be good. I’d check its documentation.
Its own instrument. As opposed to a sampled instrument running in a sampler VSTi such as Kontakt or Halion.
Check your documentation to see if you can set the MIDI channel in the instrument. If not, you would need a work-around or a different solution.