the best way to get multiple projector shutters to close at the same time is using RS232.
you can set up a TCP port and point at a netcom IP-Serial adaptor. Catalyst has preset serial strings in the custom serial device that you can use to lamp on/off and open/close shutter on a panasonic projector.

The problem with using http commands for multiple projectors is latency between each command, but it can be done. Write an applescript to tell safari to to open the URL and trigger the script from catalyst.

I've not tried calling the URL directly from the custom serial device for stuff other than catalysts own web server, but I guess it should work. You dont need to set a TCP port, set the custom serial device to "no output" and type the URL into an available preset as you would in safari.

At the moment PJ link is not supported

Hope that helps, let me know if you need more detail