[BScout]

What you are referring to as a "sub" is referring to masking. But in either case you are fine.

My guess is your ethernet priorities. I'm guessing you have more than one NIC connection on your Dell. The Dell is communicating out of say NIC1 that has actual internet access but your MTRX is hooked to NIC2. The simplest thing is avoid all this and put your MTRX on your network switch so it has a valid IP address and your Dell is only hooked to a network via 1 NIC (the same one you have data/Internet communication.) There is no downside to having the MTRX on your regular ethernet (DADman is very light on the network)

Dante is different. You can choose what NIC you want to bind communication to so it isn't using the priority NIC of the operating system (which defaults on Windows to the one that actually has internet/WAN access)

Basic troubleshooting when there are network issues is build the simplest network.