Rick Reith is currently tour managing and mixing front of house for Eric Johnson and Fuel.
Here's a technique to fatten up your front-of-house mix when using a Yamaha PM5D. Not only can compression be applied directly to the stereo bus, you can take it one step further. Patch the main left/right outputs from matrix 1/2. Assign stereo A to matrix 1/2; also assign stereo B to matrix 1/2. After adjusting your stereo to matrix levels, dial in your mix via stereo A as normal with the compressor off. With the fader at infinity, select stereo B and turn on the compression. Slowly bring the fader up under stereo A output. You will need to experiment with the compression parameters and level a little, but you can achieve a tighter, more punchy and controlled mix.