Strictly speaking the the HRI-200 is no longer needed if you just want to connect to Fusion rooms using Wires-X. All you need is a computer running a registered copy of Wires-X and an SCU-19 adapter cord that will connect directly to various Yaesu radios. This will enable you to connect to any Fusion room in the world. I do this with my FT-2 while traveling. I only need a reasonable internet connection and I'm on.
Alternately, I have a Fusion node at my home QTH. This consists of a PC running Wires-X, an HRI-200 and an FTM-400. This set-up communicates with our DR2X repeater at a mountain site. I can connect to a Fusion room and our repeater is linked into that system. Other stations can connect to my node and be heard on the repeater.
What you are trying to do is a simplex node. Stations can connect, but they will only be able to communicate with others in range of your FTM-300. I travel to Alaska (pre-COVID) several times a year and there is an operator in East Anchorage with a Fusion simplex node. I have never directly communicated with him because he is not in range of where I stay in downtown Anchorage. I have talked to him by connecting to his node.
When you use the SCU-19 cable your radio functions as an A/D and D/A converter. There is no RF involved. Thus, I connect my FT-2 to the computer running Wires-X and the radio is just a digital speaker mic. Make sure you have the most recent firmware. It is needed to use these features.
Check out
www.hamoperator.com for lots of Fusion/Wires-X information.