I would use a carrier frequency and then modulate onto that one of 3, 4, 5 or 6 different frequencies (sound up, sound down, chan up, chan down, power on, power off). The main carrier would descriminate against any other remote, and the modulation frequency would work the controls. Or, you could use dtmf, since they have a single chip that decodes the multiple frequencies for you and gives a valid output command.