The Voodoo lab also has the capability for stereo. I don't use it that way but lets say your last pedal was a stereo chorus going into the switcher. By using both inputs on the switcher that would turn outs 1&2 into left and 3&4 into right. Very cool pedal and it works great.
That pic is just for reference. The 10-band and the treble boost (first pedal) are no longer on the board. The amps sound best the less you put in front of them.
The connection to the PA really adds depth to the rig and I place the PA cabs on each side of the Marshalls angled slightly up. I use a couple of combo amp stands. The ambient delay through the mixer keeps the overall tone from being so dry. I just match the volume of the PA cabs to the volume of the amps. Actually the PA cabs are just a notch under the volume of the amps. Classic 70's stadium rock sound with my Les Paul, Strat or Flying V .