Spiff,
Actually, Dolby Labs give you about a 15-degree range back or forward of an imaginary line drawn across the listening area. If the QS8s are exactly even with you to each side, they'd be at a 90-degree angle to the front speakers. So there is flexibility. In some rooms, there might be slight differences in the surround envelopment if they were slightly behind or forward of that horizontal line across the room. And if you want the QS8s to do double duty for SACD or DVD-Audio playback, there is a persuasive case for keeping the QS8s a bit more to the rear.
With the QS8s' quadpolar driver array, I hear little difference in my own installation. Nevertheless, I always urge some experimentation. "Well above ear level when you are seated" is, in my experience, always beneficial. Just how high doesn't seem to matter much with the QS8s. But direct-radiating surrounds tend to be much "fussier" about mounting location, again depending on the room and seating arrangement.
Regards,
