I'd say, definitely get the QS8s. Place them on the side walls to the side of the couch. They seem to be very forgiving for placement so they could be positioned just slightly ahead, behind or even with the couch. If you can devise a way to experiment before drilling screw holes, it could be a fun experiment. Otherwise, you should be very happy as long as you give them some breathing room from the ceiling and the back wall.
If the door or other issues cause placement problems on the walls, you could always place them to the sides using the stands you already own.
If you can get the couch pulled out from the back wall 4' or so, you could experiment with 7.1. If I were you, I wouldn't invest in extra speakers for 7.1 right away but use a couple of your existing speakers as the rears to experiment with. You might even decide to keep the existing bookshelves as rears as they may work very well for you. Many people use direct radiating for rears together with QS style for surrounds.
In my current room, my couch was only about 3-4' from the back wall and I experimented with my old HK bookshelves as rears for 7.1. I actually went back to 5.1 with just my QS8s for surrounds. I just didn't find enough improvement.
In fact, it could have been me, but because the rears were not working very well in thier required placement, I found I was losing some surround effects that sounded better when the processor was doing straight 5.1 instead of trying to figure out what will got to my ineffective rears and what will go to the surrounds. Might have been paranoia though.
With your older speakers, pre-existing stands, and a little extra speaker wire, you are set up to have lots of fun experimenting.
The QS8s for surrounds though, are a definate must have.
