+1
I use a bus compressor in ducker mode. in the ducker, you can set the value by which the signal should be ducked. In conjunction with the threshold, you can then set the compressor to work with relatively low signals, but when the singers get louder, the signal is not suppressed any more. I get on quite well with this.
I haven’t thought of using a Dyn8 yet, mainly for the reasons John mentioned, but it would be really great if there was such a possibility.