How can I set up Cubase (or Motif ES) so that lower octaves will control one VSTi and upper octaves different VSTi?
for example I want two lower octaves to control VSTi with a Bass sounds and upper octaves to control piano and strings sound on some different VSTi, or send to different MIDI channels inside cubase.
So long as you have a version of Cubase which has the Input Transformer, use that…
Record-enable two MIDI tracks (one to each VSTi 
), and place a Local Input Transformer on each, and set one to filter out all notes above a threshold of your choice, and the other to filter out notes below the same threshold.
Cool. I’ll try that. Thanks