I use the aux's every gig for IEM mix. It works excellent, but I don't know the models of IEM their using.
I set my vocal compression lightly, with a ratio from 2:1 to 3:1 and 3-6 db gain reduction (when activated).
There's also the compressor on the aux output, but i don't use it.
that's exactly backwards!
you
don't want to compress the individual vocals in their monitors, that's what leads to over-singing and blown-out voices. that's what the big hullabaloo over V2.0 was about, the option to take that channel comp
off the auxes.
you
do want to use the aux comp, set up more like a limiter; fastest attack,
very high ratio (to where the top of the green "mountain" graph is pretty much chopped off flat), and the threshold is just high enough that it doesn't get reached with normal levels.
that way, there's no squash in the ears with normal use (preserving the singer's dynamics and their voices) but any "accidents" will hit the threshold limit and not blow anybody up.