Does the console have the feature where it flashes lights connected to X10 Wall Switch dimmers or Lamp Modules, when the alarm sounds?
If the console has a House Code and Unit Code dials. For setting the Security Light X10 Address. That is what will flash the lights if any X10 dimmer types are on that address. The same flashing commands will trigger the Powerhorns also.
Set the Powerhorns House Code and Unit Code dials to the same X10 address as the Security Light address. They should start sounding when a alarm flashes the lights.
I have never seen a specific setup for Powerhones, only the Security Light Codes. That Powerhorns also use.
I see the console does not allows you to send regular X10 On and Off Codes with manual buttons.
You maybe able to use the Lights On and Lights Off buttons. On one of the old remotes if you have one. Try sending a continuous cycle of Lights On and Lights Off commands with the buttons to the Powerhorns. After a few On Off cycles they should start to sound. That will at least see if they are functional.
I have a real old X10 product manual from an old X10 dealer in storage. I found the SS5400 information and scanned it.
Includes DW534 Door/Window Sensor, HT544 Remote, BR521 Console, PH508 Powerhorn, SP554 Motion Detector and KF574 Key Chain Remote.
I may have to do a smaller set since the one PDF file was rejected for attachments. I think my slow DSL Upload speed timed out the X10 servers time out.