Hi,
You have very helpfully published the HTTP/API control here:
http://wiki.plexapp.com/index.php/HTTP_API/Control
I'm using this very successfully from iRule to control PLEX.
However looking at Remote Buddy, this program seems to have a far bigger list of control commands for Plex, as you can see from the enclosed screenshot taken from Remote Buddy. Felix must have got them from somewhere. Do you have details for more API commands?
Hope you can help.
Thanks,
Roland