When connecting a Roland digital snake directly to a V-Mixer, a cross-over cable is required. If using a switch, straight-through or crossover can be used as long as the switch has auto-switching. The Roland S-4000M Merge contains auto-switching however if using a 3rd party switch, check the documentation for information regarding if the product contains automatic-switching and if there is a need to turn this on.
Be sure to use the highest quality Cat5e or Cat6 available. If you are making your own cross-over cables, be sure to conform to the 568A and 568B wiring standard.