Good Day, Luc -
I have not been following this thread closely, but just looked at the pictures you posted.
As to the front speakers, I would get the Axiom Full Metal Brackets (as already suggested) and follow the advice to mount the speakers away from the corner of the room. If - using temporary stands of some kind - you can experiment a bit with the placement before mounting, that would be good. However, the FMB is such a good mount (swiveling and tilting) that you should be able to compensate quite a bit if necessary. But do get them out of the corner. Perhaps about half-way between the wall and the television, with the top of the speaker one foot or so lower than your current configuration. Your ears and your room will be the only way to decide for certain.
I believe that this change alone will make a very large difference in how your system sounds.
For the Center speaker, I see that your TV is too narrow at the top to support it. I understand! There are some shelves made for this type of thing, or you could consider a stand in front of the TV. You may wish to consider also mounting the center on an Axiom FMB somewhat above its current position and angled down.
For the back, I have some experience with a room like yours (where the listening position is against the back wall). Without hesitation, I would strongly encourage you to get the QS8's (or even QS4's) and mount them flush with the wall at nearly the same position as your AX1.5's. You will not use the shelves and you will NOT need the FMB; the T-brackets that come with the speakers are ideal for your installation. Again, if you can get the right QS speaker away from the corner just a little - even by a few inches - that will be helpful.
I had my surround speakers "behind" me like this for quite a while and still found the effects to be very satisfying. Since the AX1.5's are now actually firing above your head, I think having the quadpolar QS speakers on the wall behind you will provide a tremendously positive change for you.
After studying the pictures for a while, I am convinced that most of your current discontent is due to placement.
Enjoy and please keep us posted.
