How to send external audio into a VSTi Synth?

Is there any way in Cubase to send audio into a synthesizer? I wanted to send a drum loop into the ARP 2600 from Arturia. In Ableton, as soon as I create the synth, I can route audio into it.
ARP2600 Ableton.JPG
But in Cubase it doesn’t appear in the routing section or as a send. VST effects have that button on top where you can activate external sources, for example for side chain compression. But that button is missing for the VSTi. Any ideas?

Did you try a quad bus? That used to be the old way to get sidechain into VST2 plugs. The inputs might show up there.

Can you explain a bit more what you mean? I know the quad bus can work for insert plug ins but how could it get the signal into a vst instrument?