Every time you set a pair of speakers in a different location in the audience, there will be a time delay between the musicians, the main house speakers, and any auxiliary speakers. Each one of these time delays contributes to an unfocused and 'mushy' sound for listeners. Some high end mixing consoles have built in digital signal processors to time align speaker arrays, and there are many delay and pitch shifting plugins that can be used to in all digital mixers to delay audio from a set of FX outputs.

Other than that there are only a few affordable solutions to this problem.

I chose a pair of used Behringer Shark DSP110 a feedback destroyer and delay line combination. Although they're not currently being manufactured by Behringer, they still seem to be available new on Amazon. I was able to get mine used for around $50 each on eBay.