You know that when these emulation plug-ins are created they model using a hardware unit? And the designers almost always (esp. in the case of Waves) try to be as faithful to the original hardware as possible. So you can use the included documentation (together with some effort) to help find answers to your questions. Or you can just scoff at my posts instead of taking the time to look at the information that I provided...
You asked:
I don't know the C2. The Waves plug-in GUI is modeled after the original API; see the user manual for possible release settings.
From the Waves manual:
L/R Link
Sets the percentage of linkage between the left and right channels. While in Link mode, each channel is still controlled by its own RMS detector, which prevents loading and slaving from either side.
Range
IND, 50%, 60%,70%,80%,90%,100%
Default
100%
From the API manual:
The patent-pending LINK feature is also unique to the 2500. First, there is a variable link control, ranging from IND (independent) to 50% through 100%. The variable linking allows combining of the left and right control voltages over a range, minimizing the interaction between channels, while still linking them to retain the stereo image.
From the Waves manual:
Sidechain lets you trigger the compressor using an external source, which is fed into the RMS detector and controls the compression of the input signal. Sidechain may only be used in New (Feed Forward) mode. An external sidechain trigger cannot be used in Old (Feed Back) mode; attempting to do so automatically switches the compressor to New (Feed Forward) mode.
Here are links. I won't even tell you what they are. Perhaps you'll read it should you not find someone that's willing to spoon-feed information to you a la The Matrix.
Perhaps...
API 2500 Stereo Compressor