Sidechaining basically ducks the volume of a synth (pad, bass, whatever you want) by triggering an other instrument, say a kick drum.
Put an MClass Compressor on the instrument you want to sidechain. Create a ReDrum, flip the rack and disconnect the cables. Import a kick drum into a ReDrum channel then take the output of that drum channel and put it in the sidechain input of the MClass Compressor you have just created. To get a really exaggerated pumping sound just put the compression ratio to infinity and the threshold all the way to the left. The kick drum won't come through the mix as it isn't connected to any audio output.
You can use the ReDrum and a Spider Audio Splitter to send the kick drum as a trigger signal to up to 4 different instruments with an MClass Compressor connected.
So useful its untrue.