I think that any issues caused by having your surrounds facing is different directions will be outweighed by the benefit of raising them up and improving their ability to radiate ambient sound. Also, you could always try mounting both of them on the back wall as several members have done that to good effect. In my first room I found the best place for my 2 QS8s was in the back corners with the tweeters facing parallel to each wall. Though this goes against the general principle of not corner loading speakers I found that it didn’t colour the sound from them in any way (though my receiver detected them as larger than they were).
I would certainly advise that you could temporaraly increase the height by putting the stands on boxes and have a listen. I just wouldn’t leave them that way unless you can come up with some way to anchor them to the wall.
Depending on what your wife will put up with you could put up shelves on the back wall with a hole cut in for the bottom firing driver. That way you could play with angling them into the room or toward you seating and try to dial in the best possition. Having a shelf rail would also let you adjust the height to whatever you find optimal for your situation.
However, the QS8s are very forgiving of placement and I really don’t think you would have any problems with the side wall rear wall setup you are considering.
Cheers,
Dean
