I'm trying to get the PC4K Comp set up as a side-chain on an aux track in a project. I couldn't get it to work so I added a new normal track and tried to set up the same thing and it did indeed work, here is a picture of the setup: 


 
In the image, you can see a drop-down menu where I'm looking at a list of possible sends. What I don't get is why the side-chain input on the aux track is labeled "Track Compressor(Input 2)-Aux 1" and on the new test track (Track 14 which has working side-chain functionality) the input is labeled "Built In Channel Fx(Input 2)-Track 14"  I'm wondering if for some reason Sonar is handling the exact same compressor two different ways.

Ok, so now I know with the aux track soloed the side-chain wasn't working. Still a little confusing with the naming though.

Hey Scott, I did a quick test, and, at a minimum, it looks like a bug in the naming of the sidechain input when the Aux track sidechain input is created first. When I created the ordinary track first, both sidechain inputs ended up being named for the plugin exposing the input as expected. I didn't have time to test whether the sidechain was working on the Aux track.