I have the QS4v2. They are excellent. They achieve the same goals as the QS8 which is a non-directional (its hard to tell that the surround material is coming from the speakers) "enveloping" sound. The QS8 have more power handling which is suitable for larger rooms and people with power amps, due to the larger cabinet and driver, different crossover point and goes just a tad bit deeper. However, you don't run surrounds full range anyway.
If you have a variable crossover point setting for each speaker on your AVR, I would set the QS4's crossover point between 80hz - 100hz
