What are the main differences between the 640/641 and 640m/641m?
The “0” suffix models have a display panel and controls, whereas the “1” suffix models lack a front panel display.
The “M” suffix variants have 4 Mic Line balanced/unbalanced inputs as opposed to the 2 on the standard model. Also they have an Ethernet port for configuration and can be configured to operate as a mixer in Mix Mode.
All non “M” suffix models are capable of routing single sources to an output. “M” Models are capable of both routing and mixing multiple sources to an output.