Without knowing any specifics of the
system, I would try to get as much discrete control over the rig as you possibly can and not discount the Center
Cluster for just SFX. Do you have any Front Fills? Can you get Front Fills? Just having a single "Master'
send to a
system really is an unfortunate position to be in. You can EQ all day and all night, but at the end of the day, this entire thing is one big
speaker positioning problem and EQ will only
cover up problems.
I'm going to assume this is a musical, or music performance. In those cases, I lean on my Center
Cluster the heaviest -- this is what is punching my vocals through to the bulk of the theater (if it was designed correctly). It also images the most correctly to the majority of the
stage (again, if designed correctly). The L/R pushes the majority of my band, and does some light vocal fill-in. Then from there I have Front-Fills that are reinforcing the Center
Cluster, because typically the way physics works, sound from the performer will get to the front row before sound from my
cluster so I need speakers even closer, plus in a
thrust I can aim my bottom CC box off the
thrust, and then fill in around the
thrust with FF and Side-Fill.
For reference, in a moderate sizes
thrust I typically design an "exploded" center
cluster, typically some small format
line-array that does the center section of the theater, and then some point-source boxes left and right of this
cluster, filling in the L/R sections - but all getting the same signal as the
array. This all pushes my vocals out, and then the
Front Fill system compliments the Center
Cluster system.
If you have no access to other speakers than this L/C/R I would look at what sort of
spill you're getting from the VRX onstage, and see if either removing the bottom box and using it in a more advantageous position or just unplugging it helps clean the
stage up a
bit.
The bigger issue aside from
feedback is really coherence. With your speakers behind the performer, the sound from the speakers will always arrive at the destination before the speakers which makes your coherence all wonky. Your only three options are 1. to accept this, or to 2. make your PA a lot louder than the source material or 3. add in a thousand speakers (see
this on Natasha Pierre if you want to know what happens when your entire theater is suddenly a
stage).
On the flipside, if you notice you're notching the same frequencies out of every mic, you want to un-do that from every
channel and do that on a mix, assuming mixes are set up in a coherent fashion to make this possible. Generally my musical theater
console structure has a variety of
Vox mixes (Vox-M Principal, Vox-F Principal, Vox-M Ens, Vox-F, Ens, or if I'm lucky to have a
desk with auxes for days, I'll double that number and have "heads" and "ears" auxes on top, for ear rig mics and mics in hair.
