controlling multiple 8x8 RGB LED matrix

I disagree - the use of Shutdown mode and diodes to isolate the cathode drivers will allow one MAX7219 at a time to control the cathodes.

[EDIT]March 2014 - just had a discussion with someone trying to use this schematic - turns out I have the diodes on the individual segment outputs, when I intended them to be on the shared common cathode digit outputs.[/EDIT]