In my other DAWs I'm used to being able to do the following:
 
- create an AUX bus
- insert a couple of effect plugins on the bus
- insert a compressor at the end of the chain (or somewhere in between, depending on the intended goal)
- send from another track (e.g. vocal) to the sidechain input of the compressor
 
In Sonar I cannot find a way to do that. It seems that Sonar lacks native VST3 sidechaining support?! Is that true? Do I have to set up a complex routing scenario with multiple busses to simulate the intended behavior, or is there a simpler way that I don't see?

Sonar does sidechain support with any VST3s that support it and with its own (DXi) Sonitus compressor/gate. Once you've inserted a compatible plug, it should show up in the list of available sends.

Strange, I do not see anything in the sends list that looks like a sidechain input. Of course, sidechaining is enabled on the plugin in question ...
 
I'll investigate some more ...
 
 

Which compressor are you trying to use?

You don't need to enable sidechaining on the plug-ins with SONAR, either they have it or not. If they do, then the sidechain input should show up as another track's available send.
 
I'd suggest starting with the Sonitus Gate or Compressor to get a feel for how the process works in SONAR.

Sanderxpander
Which compressor are you trying to use?

FabFilter Pro-C in this case.

Anderton
You don't need to enable sidechaining on the plug-ins with SONAR, either they have it or not. If they do, then the sidechain input should show up as another track's available send.
 
I'd suggest starting with the Sonitus Gate or Compressor to get a feel for how the process works in SONAR.

Thanks for the suggestion. I'll have lunch now, and then I'll check if I overlooked something.

Pro-C working fine here. Do you have the latest version? Actually I think it hasn't been updated in ages but it seems worth checking.

I am not sure how it works in your other DAWs but make sure you set up the compressor on the track you want "ducked" (or whatever you are doing) and then the send will show up in the send list of the track (eg kick drum) of the track you want to send to the input of the compressor (which sounds like exactly what you are doing)

I haven't tried sending a TRACK send to a BUS Sidechain compressor - i guess it would work the same but could this be where things are going a bit different as you mentioned an aux bus?

Everything is fine, thanks, guys - I simply did not find the send because Sonar does not mark it as a sidechain input. That's different in other DAWs, and I did not realize that.