Keep it simple. Cherry Sub Amp. I agree the main speaker should go down to a minimum of 28HZ or so as the piano does. However I like Organ music very much. So for me the speaker needs to -3db at 18hz.
I cannot see buying a speaker that does not go at a minimum of 30hz to a max of 18hz. That would be accurate in phase bass. As long as your room can support low bass your in if not no bass for you