What is the difference between the M models and the S models?
There are two types of PPM: Mono and Stereo. The Stereo version allows you to have stereo image in your main speakers (when the Power Amp Routing button is OUT); you can pan the sounds left and right (i.e. guitar on the left side, vocals in the middle, etc). The Mono version does not allow you to pan your mix; it is the same sound through all the speakers. When the Power Amp Routing button is pressed IN the units are virtually identical. Also of note: the S series has two mixer outs on the front panel, while the M only has one; the S also has stereo inputs on channel 7 and 8, while the M has dual mono inputs (except the 406M which has none at all).
