I just went down to measure as you had me curious, I have 5 1/2 inches from the top woofer to the ceiling. Here is another pic from behind when I had mansfield beach Qs8's. The shelf bracket worked great as I was able to conceal my wiring nicely.
Axiom also makes a Qs8 ceiling bracket that will let you angle the Q's down slightly. I believe Alan as mentioned on many posts that you should try to have close to 4" if possible, but some people have gone closer. If your saying that you could mount them below that beam about 2-3ft in from the wall, that might work. The beam does not look that wide so it might not cause to much problems with bass.
My ceilings are 9ft tall in the basement, so the boxed in area is about 8.2ft off the ground. I think the bottom of my qs8's are around 7ft off the ground.
