OP Here. For me, the two key things are room mics and stereo mix. I have 2 PZM mics that I picked up off ebay for the room. I play guitar stage left, so I pan my guitar slightly left and the other guitar slightly right. Vocals, bass and kick are centered. I don’t mic the guitars anymore, we both use a DI so my IEMs always have a consistent signal.
Doing these two things made a world of difference for me.
I would also be interested in compression settings for IEMs.