Mid-level combining methods and systems that combine benefits of high level and low level combining methods for generating HD (High Definition) radio signal outputs. The High level IBOC combining technique combines the RF outputs of an analog transmitter with an IBOC transmitter operating in a combined digital/analog mode, and can include a properly phased, identical, analog component of the signal feeding the analog transmitter. The low level combining technique includes splitting and phase adjustment for the purpose of feeding the analog signal simultaneously to an analog transmitter and an IBOC digital transmitter operating in a combined digital/analog mode. The mid-level combining method and system uses attributes of the high and low level methods and systems. Another mid-level combining method and system is for high transmitter power output (TPO). Additional methods and systems for converting existing transmitter room spaces to HD (High Definition) radio transmitters, without having to add onto existing rooms and buildings.