My system right now consists of just the TV, sat box, and audio system.
The only functions used on the TV are on/off.
The only function used on the sat box is "change channel".
The only functions used on the audio system are vol up/vol down.
The only function managed by MythTV is changing channels, everything else is handled by the devices normal IR remotes. The TV has no connection to the sat box; that is to say live tv is managed through MythTV and only MythTV. I should imagine it would become very confusing very quickly with multi-room setups if AV equipment was connected directly to each other rather than routed through LinuxMCE... If live tv is not or cannot be managed by LinuxMCE in the same manner as MythTV (on disk ring buffer for pausing, etc), then I will stop right here, that is the primary use of the system. I accidently hit the "TV" option once in the UI and it attempted to launch MythTV though so I assume it works as I expect.
With all that in mind, I see no reason to implement anything other than the sat box "change channel" command at this time, since I am only looking for equivalent functionality from the setup. I dont even have the possibility to control any of the other equipment yet, as they have no serial or usb interfaces and I do not have any IR transmitters. While there are 10 key commands in the protocol, I am worried about performance of the sat box in this case. It is painfully slow to respond to them on the remote.