The rear speakers of the q950a are quite heavy, but these stands are enough in my opinion. Even though Samsung recommends stands rated for 8kg load and these are up to 5kg, the speakers are actually just about 1.5kg or so each. They are big however co the center of mass is to be considered. I mounted mine with screws "Schraube Rundkopf 1/4 Zoll UNC 14mm Gewinde Chromstahl A3 Innensechskant" bought from swissphotoshop dot ch and they are fine. The whole thing is a bit inclined forward, but it is actually the way I wanted so it's fine. You might want to experiment with mounting the speakers on the flat bases that are included with these stands, this way the balance issues should be mitigated.

I now have a HW Q950A, but how did you do it with the cables? Have you "customised" the power cable of the rear speakers or do you just have the cables outside in front of the stands? Who can answer that for me?

Yes, it fits. I use the stands for the rear speakers and I am very satisfied.