Question:  Does the HMS-4X need to be on the same subnet as the HRM-4X to work? Or can they be on different subnets?
Answer:  Connecting a HelixNet system to an existing IP network requires planning with your IT department in order to plan the IP addressing scheme. 
By default HelixNet Main Station uses automatic IP addressing (DHCP) enabled. In order for that to work properly in an existing IP network there must be a DHCP server handing out IP addresses. If no DHCP server is found, a Main Station will revert to an unused link-local address in the 169.254.0.0/16 block.
Through the Networking menu you can disable DHCP and set static IP addresses. When you assign static IP addresses you need to make sure that the Main Stations you want to link together are part of the same subnet.
A HelixNet mainstation linking to another HelixNet mainstation: Requires that both units are on the same subnet A HelixNet mainstation linking to a HelixNet Remote station: The Helixnet Remote station (or remote speaker station) can be on a different subnet