Plex HTPC still comes with CEC support, just like PMP did.
{
"name": "HDMI CEC",
"idmatcher": "CEC.*",
"mapping": {
"KEY_LEFT": "left",
"KEY_RIGHT": "right",
"KEY_UP": "up",
"KEY_DOWN": "down",
"KEY_SELECT": "enter",
"KEY_BACK": "back",
"KEY_PLAY": "play",
"KEY_STOP": "stop",
"KEY_PAUSE": "pause",
"KEY_SEEKFWD": "seek_forward",
"KEY_SEEKBCK": "seek_backward",
"KEY_SUBTITLES": "cycle_subtitles",
"KEY_NEXT": "step_forward",
"KEY_PREV": "step_backward",
"KEY_HOME": "home",
"KEY_NUMERIC_([0-9])": "%1"
}
}
As long as all your buttons appear in some way in the log file of Plex HTPC, you can even extend the number of supported buttons: Create your own inputmap | Plex Support