What kind of set up would I need to have the monitor sound control levels muted without having to go behind the speaker to turn down the volume? Is there a button I'm not seeing on the Tascam DP 24SD?
There's the Monitor Level knob on the top panel. It also controls the headphone level. You could use a line level switcher between the monitor outs and the speakers, and leave one pair of outputs empty. That would let you silence the monitors while still hearing the phones.