This seems like such an obvious oversight that I am puzzled why it's not already here, and not sure how to explain it further. But compressor and gate key source REALLY needs the option to specify a group or a bus! We've gotta be able to drive a ducker with more than one channel, without rigging up a feedback loop with patch cables, and it seems completely obvious that somebody might want to drive a sidechain with more than one channel at a time!