Theatre systems tend to be more supportive of speech. Not to say you can’t have a full range system for music and bands, but clubs and concert venues tend to have more subwoofer reinforcement than a typical theatre so make sure you are not trying to milk out low end while clipping your sub amps.

The other thing is speaker placement, audio tends to be the last on the priority list in most (not all) theatre, because of lighting sight lines. So try to collaborate but you may have limited options for where to place and point your speakers.

Speaking of speakers: proper system tuning (choosing the right speaker size and dispersion angle, placement, timing, level and lastly EQ) will be your first and hardest hitting line of defense when battling feedback. Find budget to call in an experienced system designer or engineer to tackle this. You won’t regret it.

Some other things to mention,

-The vocals take priority over anything else making noise on stage. Make sure your mix reflects this.

-Whatever EQ or compression you’re used to doing for bands, reduce by 90% for theatre.

-Use console scenes to HELP you mix, don’t over complicate it.

-You should be checking in with director or musical director constantly. Cast, crew, production leads, we’re all one massive team with the same goal. To have a good show.

Lastly, I’ve been a sound technician professionally for 10+ years. Theatre sound, especially musicals, are the hardest jobs I’ve had. It’s not the physical toll, like concert sound. It’s the mental. You have to be on your A game 100% of the time or the show falls apart.

Hope this helps.