I connected my Dakota Alert WR-3000 receiver to an EZIO6I, which has Inputs like the EZIO2X4, just more of them. Connect I1+ on the EZIO2X4 to +5V on the EZIO2X4. Connect the Dakota Alert receiver relay N/O contact and COM for the “zone” you are using between the GND and I1- on the EZIO2X4. When the relay closes in the Dakota Alert receiver, GND is applied to I1- causing Input 1 in the EZIO2X4 to turn ON, sending a Insteon ON command to whatever Insteon device has been “linked” to Input 1 of the EZIO2X4. When the relay opens, GND is removed from I1-, causing Input 1 to turn OFF and the EZIO2X4 to send an Insteon OFF command to the Input 1 “linked” device. The Dakota Alert WR-3000 also has a 12V source for Zone 1 which can be connected to Input 1 on the EZIO2X4. OUT to I1- and 12V to I1+. I chose to use the relay contacts so I could connect each of the four Dakota Alert zones to a different EZIO2X4 (actually an EZIO6I) Input. That is the easy part.
Insteon protocol is much more reliable than X10 because commands are directed to and from specific Insteon device addresses (xx.xx.xx) and those commands are acknowledged and repeated if they fail due to noise on the power line. This protocol reliability comes with the price that it is more complex to set up an Insteon network. Although in theory an application could just “poll” a specific Insteon device address to determine the device status, mcontrol does not do that (per the mcontrol V2.1 Users Guide) because of the added traffic that would put on an Insteon network. The EZIO2X4 must be linked with some other Insteon device so that the EZIO2X4 Insteon address (xx.xx.xx) will appear in an Insteon PLC device Link Database (per the mcontrol V2.1 Users Guide). Again, from the mcontrol V2.1 Users Guide, only Insteon device addresses in the PLC Link Database are monitored for device status changes. Linking Insteon devices can be done using a software program like Smarthome’s “Houselinc Desktop” (and others) or done manually using “Set” button procedures documented for each Insteon device. Each Insteon device comes with a Quick Start Guide that describes how to link the specific device. Simplehomenet provides a free downloadable Simplehomenet Utility Suite that runs on a PC. It can be used to programmatically set “links” in the EZIO2X4 and whatever Insteon device you will link to. It communicates with Insteon devices plugged into the power line through a Smarthome PLC or Simplehomenet EZBridge or Simplehomenet EZServ device.
You will have to ask mcontrol about defining an EZIO2X4 device type. The mcontrol V2.1 Users Guide only listed the Irrigation Controller under Simplehomenet devices supported but I have found that documentation often does not keep up with devices actually supported. When you mentioned you wanted an X10 command sent to your X10 sounder, I presume you want the mcontrol macro to do that. The EZIO2X4 does not support assigning an X10 address to the Inputs. At least that is the way I read the Quick Start Guide for the EZIO2X4. Only the 2 Outputs can be programmed to respond to X10 commands.
The Insteon device protocol requires more work to get devices up and running but once done, you will find that those devices are much more reliable than the old X10 stuff. I had X10 throughout the house, installed the best coupler/repeaters I could buy, and never came close to the reliability I see with the Insteon devices.