I just created a new project with three 'instruments', each with their own (virtual) keyboards :
(Kirnu is an arpeggiator and I used Simple Instrument Tracks for all components, MIDI Output enabled)
Intrument 1A. Kirnu 1
Input : "Sonar Virtual Controller / MIDI Omni"
Output : "None".
B. Rapture
Input : "Kirnu 1 / MIDI Omni"
Output : Master
Instrument 2 A. Kirnu 2
Input : "1.Internal MIDI / MIDI Omni" [which is loopBe30 Port 1]
(to which is connected the Chirp virtual keyboard)
Output : "None"
B. SI-Electric Piano
Input : "Kirnu 2 / MIDI Omni"
Output : Master
Instrument 3Dimension Pro
Input : "2.Internal MIDI / MIDI Omni" [loopBe30 Port 2]
(to which is connected the Granucon virtual keyboard)
Output : Master
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I play notes into Kirnu 1 in 'Hold' mode so they latch and Rapture plays them non-stop.
I play notes into Kirnu 2 also in Hold mode and SI-EP plays them non-stop.
I then play Dimension Pro freehand.
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I encounter no crosstalk between instruments. I can play notes on any of the three keyboards while everything is running and there is not confusion between the instruments.