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.
Being fairly new to IEM's, I have not yet had any issues with over-singing or blown out voices. My singers are pro's, and sing at a very even level each night, so we've never had a problem. By using the channel compressors lightly, they hear what I hear. I had not thought about putting a limiter on the aux out's, but that is an excellent idea. I've never needed it for live monitors, so I've just mixed IEM's the same. I'll give it a try at the next gig.
Regarding pre/post DSP, I've completely changed my thinking on this, as a result of owning this board. I've learned that if I make EQ adjustments to a particular channel, that needs to be heard in the monitor as well. You can't fix individual channels with the aux 31 band EQ, so at this point I prefer the channel EQ to be heard in the IEM. I'm using the channel comp's very lightly, and my band loves the IEM's, so I must be doing something right! (I'm going to try the aux limiters at the next gig)