The pictures below show the MIDI and audio routing into and out of 2 well-known multi-timbral VSTis - Kontakt (v4) and SampleTank 2.5.
Both VSTis offer internal routing possibilities too, but these should get you started.
For Kontakt 4 8-out with the excess MIDI channels deleted.
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https://i.imgur.com/0UCwuBi.png
and, for SampleTank 2.5.
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https://i.imgur.com/6gjhLIC.jpg