After that, I'm going to plug in some instruments and begin mixing my sound. The last time we hooked this up, we had a channel that would never fully mute. Even if you muted it on the mixer, you could always hear it through the monitors. I want to tackle that.
Ahhh, sounds like the "Pre" button is pressed. From 2.1.3 of your manual:
"(10) Press the PRE switch to set all aux sends to pre-fader. In this case, the volume of the aux signals is no longer depen- dent on the fader position, so you can create completely independent monitor mixes."
When the "Pre" button is engaged on that channel strip (and they are all able to be set independently), the fader position does not affect the Aux send (i.e. what you are sending to the monitors). This is helpful if, say, you want to be able to "Talkback" to the stage, and have your "Talkback" not going into the house while people are there, but if it's engaged, you would also have this problem- the instrument/source is playing through the monitors but isn't in the house, and you feel like you can't make it shut up!
When the "Pre" button is disengaged (now called "Post-Fader," or "Post" for short), the levels in the monitors will be additionally controlled by the fader position. So, if fader is all the way up to normal levels, you'll have monitors rocking as well. When you pull fader down/mute, the monitors go quiet as well.
Another one of these fun things to play with!
Ray