PSR01 is part of the X10Pro series.
Can you give us the systems model number and are the Powerhorns the PSH01 or PSH02?
The Powerhorn is not turned on by a single O command to its address, but a series of All Lights On;All Lights Off [All Units Off also works] or a series of On; Off commands to the address it is set to. So you may want to try the Security Light Address.
I will see if I can find more details on the remote and edit as I find data.
Try a series of All Lights On All; Lights Off from the Security Keychain Remote. Should be about one second apart. After three to four cycles. They should start making noise. They will continue as long as the cycles continue, and then time out in about four seconds after the cycles stop.
Maybe the X10 Instructions may help you.
ftp://ftp.x10.com/pub/manuals/sh624-is.pdfLooks like the buttons are Units one through four. Using the House Code on the dial. So if you set the PowerHorns to A1 Try alternating On and Off buttons on your remote. Again one second intervals and takes maybe four or more cycles to start them.