brconflict
Waves doesn't provide an easy way to enable side-chain inputs on their own plug-ins. I still have problems trying to make it work, even after watching videos on how to. I know this isn't helping, but I'd honestly like to see a video that addresses this, specifically. I simply use the Sonar-supplied plug-ins to achieve this now.
Maybe I'm not understanding you correctly, but there's nothing that you need to do to enable sidechaining on Waves plugins (or any other plugins that support sidechaining) in Sonar. Unlike PT, Studio One, etc., there is no button to activate the sidechain input on a Waves plugins. In Sonar, all you need to do is insert the Waves plugin on the track that you want, say, ducked. Then, the Waves plugin will appear in the list of destinations in your other track/send outputs. So, here's a simple example, since I can't create a video right now:
1) insert Waves C1 in the FX bin of the track that you want ducked by the kick drum
2) in the kick drum track, click on the output dropdown menu and select Waves C1 as the output destination (note that this will silence the kick drum so, alternatively, insert a send from the kick drum track and choose Waves C1 as the destination)
3) open the C1 GUI and adjust the parameters (e.g., threshold, ration, attack, release) until you get the desired level of ducking
Also, make sure that you are using the VST3 version of Waves (or FabFilter, etc.) plugins - VST2 won't work.