I am not the OP but the problem I have been trying to fix is when doing a musical theater show there are times when the teenage girls all singing together get loud and screechy. The loud part is supposed to be that way the screechy part isn’t, it is due to lack of training and talent in general. I have been using 2 Midas M32 mixers for these shows and I have used the Combinator in these mixers which seems to be a multiband compressor and it helps but I think I could do better with a Dynamic EQ instead. But that is not available in these mixers.
I do not recognize "screechy" as an objective technical description.
You suggest it has something to do with technique and experience so can I speculate it is dissonance from poor harmony? I don't know how to mitigate that with dynamic level or eq processing.
Is it possible to give the best singer in the group more level and the lesser singers less level, to reduce the interference which is worst case for all getting equal level. Of course this is just a WAG. Maybe you could capture a multitrack recording of the crew and mess around offline with alternate remedies.
I feel I am in general a purist and always shoot for what goes in is what comes out. I have never felt the need for a Dynamic EQ or a Multiband compressor in any concert work I do just in the theatrical shows.
Good luck but some things are difficult to fix even with technology..
JR
PS: FWIW last century I speculated about "smart" mixing systems that could read the mind of inexperienced operators, and give them what they didn't even know they wanted. EQ and mix levels would target a template of some common (good) musical mixes. Of course this was impractical, because entry level inexperienced operators are unwilling and incapable of paying the premium prices such processing power would require.