The M32 consoles all feature 6 dedicated matrix channels. Matrices are, in essence, 'buses' for MixBuses. Channels can be fed to MixBuses, MixBuses can be fed to Matrices. Also, a popular usage for Matrices would be to send the L/R to two Matrices for delay stacks, or for another zone. This will give you a separate volume control for the other feed. See the video below for some quick tips on set up and use of the Matrices.
Keywords: M32, M32R, M32C, M32 Live, M32R Live, M Series, Matrices, Matrix