It doesn't appear to me that the rear wall would have any significant effect - maybe a slight loss of volume on the left side due to the lack of wall immediately behind.
With the new baby, I went ahead and wall mounted my QS8s 8' high (9' ceilings), 5' behind the LP, and 10' to either side of the LP. Previously, they were on stands that I would position a few feet behind the LP, about ear level and much closer to the LP. The result is a significant decrease in the diffuse, enveloping effect created by the dipole design; an increase in the surround spkr volume levels; and a huge increase in the convenience factor.
I forgot your question, but the QS8s are awesome when optimally placed and still pretty damned impressive in botched up placements like mine.
