Mike, welcome. Although room volume and listening distance are both factors which affect the acoustic output(and power input)needed from speakers, the listening distance is far more significant in rooms of the sizes found in typical homes. The general magnitude of the effect, as determined from measurements by Dr. Toole and others, is that sound levels drop off about 3dB per doubling of listener distance(i.e., requiring a doubling of power input for a doubling of distance).
In your described setup, the listening distance would be just a bit longer than the basic one meter standard distance for sensitivity ratings. The QS4s would likely satisfy your listening needs, unless you wanted to listen at dangerously(to your hearing)high levels.
If possible, the QSs in a 7.1 setup should be placed directly to the side of the listening position and 2-3' above ear level.
