Hi avdude,
If you listen in the sweet spot using your M3s as surrounds and substitute QS8s, you won't hear a dramatic difference, however, as soon you move to any other seat, even shifting your seat on a couch, you'll get a much more enveloping surround field that's highly convincing anywhere in the room.
I also find that with really good stereo (decoded in PLIIx, Logic7 or dts Neo:6) or multichannel classical recordings the QS8s deliver a superior sense of "hall sound" than direct-radiating surrounds.
Regards,
