Stephane, what you describe sounds like the problem I originally had in my basement HT room. It was all one big huge room. The HT area was over in one of the corners, so I had a front wall, left wall, back wall, but NO right wall. It just opened up into the bigger overall room.
I ended up making a "bump out" wall on the right hand side which is about 6+ feet. I ended up making this into a closet area so I could easily get to the back of my AV gear. Plus it gave us extra storage. It also helped to set my screen back and looks better. Here is a picture of the right side, you can see the bump out closet I built along that entire wall...
Randy
