Do you guys use a sound man? It's always good to have someone at the controls.
I think you have 4 aux outs of your mixer, that's probably what I would use if you're not using them all for monitor mixes. I assume you guys play a lot of clubs like we do, not terribly big and rooms where amps can more or less carry a room. Tapping the main out may not yield a great result as amplified instruments won't be that prominent in the main mix and things like acoustic guitars, keyboards, vocals, etc.
If you can use two aux outs even better, you can run a stereo mix or run vocals out of one, everything else out of the other, or whatever makes most sense to your ears.