Where do you connect wires from mixer to stage monitors

Without knowing what make and model of the gear you're looking to connect, I can't give you a definitive answer. However, in general, if you have a powered PA mixer, meaning it has both a mixer section and a power amp section in a single box, the main speaker outputs will be on the rear panel of the box and marked as such. There will also be a jack for monitors, but some mixers have an amp for monitors, some just have an output for the monitor mix, but not an amp for them, and on some you can switch the main outputs to feed either a Left and a Right speaker, or a front mono speaker and a montior speaker. Instruments will go into the individual channel inputs.

Good luck. Your mixer only has one aux out to supply only one stage monitor out. Only way to make it work would be to use the panning controls of each channel to different outputs to the Left and Right main outs for stage monitors and aux out as front of house speakers. I would get another separate mixer for monitor such as another efx 12 with every input connected to both mixers, then use the panning and main outputs to that. Sorry. Just not enough of mixer. You need an aux out for each individual's monitor.

An external equalizer will not help this at all. The problem is likely within the amp (feeding the main speakers), the connections from the board to the amp, or the speakers themselves. In other words, the answer would be "NO." Best of luck!

Without more information of your speakers and amps we can't really help you. The Mackie board puts out line-level signals and that should drive any connected amp or powered speaker to the full capability. Make sure you are using BALANCED interconnect lines either XLR or TRS cables. Use of TS unbalanced cables costs you 6 DB and also noise pickup. Make sure ALL your gear, amps, speakers etc are powered from a SINGLE receptacle or power conditioning module. Normally you will use the AUX outputs of the mixer by way of TRS cables or balanced lines in a snake to power amplifiers onstage which then connect to the stage monitors. If you have powered monitors the returns of the aux to the stage go to the powered monitors. A heavy duty extension cord brings power back from thee stage power to the mixer.

Oh my... the EMX512SC does NOT have any "sub busses" there fore there is no way to just hear YOUR vocals where there are other vocal present. The way to connect this is to run YOUR mic into the B205D and then run the line output that is intended to run to other B205D's from the B205D into a channel of the EMX512SC.

You would connect at Aux outs of Mackie to inputs of Peavey

ALL the speakers will either have to be POWERED or have external amplifiers. The mixer has NO power amps capable of driving speakers. When connecting, make sure that the mixer is powered by the same receptacle as the speakers or amps. Used balanced line for interconnection.

Buy a powered stage monitor and gonnect to the MON jack. You will select the channels to go to the monitor with the AUX knobs and the overall level with the MON slider.

Use BALANCED lines to the powered monitor... This is a TRS plug at the mixer end for sure...

REMEMBER to power ALL interconnected equipment from the same receptaacle or source, even if it means running an extension from where your speakers are plugged in to the mixer !!! The ground bounce between power receptacles within a building can destroy your equipment's sensitive input circuits.

You didn't mention what brand powered mixer you have, HOWEVER MOST powered mixers also have a line level monitor and main output jacks. These are almost always 1/4 inch jacks. In any case you should be using BALANCED lines to the powered speakers using either XLR or TRS connectors on the ends. Please tell us what powered mixer you have so we can give you better answer regarding which connections to use. IF for some reason your mixer does NOT have line level outputs, you can use a high level Direct Box to condition the powered outputs to be sent to the powered speakers..
Also make sure ALL your interconnected equipment is powered by the same receptacle or source to avoid damaging due to ground bounce on utility lines and circuits. This often means running an extension cord from the stage where the powered speakers are along with a snake of the audio cables.

You will need at least a 24 channel mixer to give you spare channels. You also need an active crossover and a snake. The advice you need is too much to include here so I am including some links:http://mixonline.com/live/FixIts/, http://en.wikipedia.org/wiki/Live_sound_mixing, http://mixinglivesound.com/blog/tag/outdoor-concerts/,http://mixinglivesound.com/blog/, and http://www.scribd.com/doc/11435651/Beginners-Guide-to-Mixing-Sound. You may need more monitors than you are planning on and you might consider in ear monitoring.