Not to diss your setup Desktop, but you might wanna move that sub away from your CPU. Low frequencies are non-directional, so no matter where you put it, it will sound the same... possibly better. I would suggest you put it behind your desk parallel to the wall, or if possible, in the corner of the room (best option). Reason: Magnetism will take out your PC in no time and being in the corner will disperse the waves better.
Another tip: put your center channel speaker behind or below your monitor. I see that it kinda dips down... put it in there maybe. You could leave the front L/R as they are, and aim the Rear Right firing towards the wall to your right and the Left Right firing towards the wall to your left. This won't be completely accurate, but those waves will bounce off the opposing walls and come back to your ears as "surround".