Hi etc6849,
I just registred to post here because I have also been searching for the IP control protocol for Panasonic TV's with no success, and I just recently managed to reverse engineer the protocol. Could perhaps save you a bit of work
I was using the iPhone VIERA remote and captured the packets it sent to the TV, and it is using SOAP (looks to be using some proprietary Panasonic extensions to the DLNA protocol, but I don't know much about that so I'm not sure)
This is an example of a request send for the MUTE key:
http://pastebin.com/h2DQMRxs
10.0.1.155 is the IP of the television I am using, and the code for the key is NRC_MUTE-ONOFF
The application only seems to be capable of sending commands that the (normal) remote control can also send. Unfortunately this looks to mean that it is not possible for instance to switch to a specific input.
All key send actions begin with NRC_ followed by the command, and either -ON, -OFF, or -ONOFF at the end. ONOFF does the same as clicking the key would usually do. ON makes the key "stuck" until an OFF command is sent. For instance, if "NRC_VOLDOWN_ON" is sent, the volume will turn all the way down by itself.
I have created a PHP class for sending the commands. You probably can't use this, but it should clarify the syntax necessary. It also contains a list of commands that I captured from the iPhone application, as well as a few that I extracted from disassembling the application itself. Most of these didn't have any effect on my television, but a few of them did. This may mean that there are other commands that can be used but which we do not know about - since I have't been able to find any description of this protocol elsewhere though, it may be difficult to find them.
PHP class link:
http://pastebin.com/wQJPKLbU
The sending of remote control keys that I described above (the SOAP action) is called X_SendKey. There also exists a function called X_String which can send a string to the TV - this only does anything if you are in a place where text can be input, like the Youtube application.
Additionally the TV also supports a subset of the normal DNLA protocol which could be usefull for control - you are able to read the volume level and set it to a specific number, as well as mute the TV.
My TV is a TX-P46G30Y. It doesn't support the newest functions of the iPhone control app (web browser, cursor control, gamepad control) so I was not able to look at the syntax for those.
If you have any questions just ask - I'm pretty sure I haven't discovered everything there is to know about this protocol, but seeing as there doesn't appear to be any information out there regaring it I was hoping it might come in handy for you.