NB, welcome. Of course the rear surrounds can't produce sound if no signal is sent to them. There's still very little actual discrete 7.1 material and so, yes, to use all your speakers you should apply processing such as DPLIIx with both 2-channel and 5.1 material to put them to work. "Simulate" perhaps isn't the best description of the process, since only the natural rear ambience mixed into the front channels or side surround channels is extracted and sent to the back surrounds where it belongs. Nothing artificial is added, but what's already there is reproduced a little more realistically.
